Intersect sql examples. Operator for INTERSECT data sets
- specifying the tables to be joined (including subqueries) in the FROM clause of the SELECT statement. First, the tables are joined, and only then the conditions specified by the WHERE clause are applied to the resulting set, aggregation defined by the GROUP BY clause, data ordering, etc.;
- defining the union of the result sets obtained by processing the SELECT statement. In this case, two SELECT statements are connected by the phrase UNION, INTERSECT, EXCEPT or CORRESPONDING.
UNION
Phrase UNION combines the results of two queries according to the following rules:
The standard does not impose any restrictions on the ordering of rows in the result set. Thus, some DBMSs first display the result of the first query, and then the result of the second query. The Oracle DBMS automatically sorts records by the first column specified, even if no index has been created for it.
To explicitly specify the required sort order, use the ORDER BY clause. In this case, you can use both the column name and its number (Fig. 4.3).
Rice. 4.3.
Phrase UNION ALL performs a union of two subqueries similar to a UNION clause, with the following exceptions:
- matching rows are not removed from the generated result set;
- merged queries are displayed in the result set sequentially without ordering.
When merging more than two queries, you can use parentheses to change the order in which the join operation is performed (Figure 4.4).
Rice. 4.4.
INTERSECT association
Phrase INTERSECT allows you to select only those rows that are present in each result set being merged. In Fig. 4.5 shows an example of combining queries as intersecting sets.
Rice. 4.5.
EXCEPT join
Phrase EXCEPT allows you to select only those rows that are present in the first result set being merged but not in the second result set.
Phrases INTERSECT And EXCEPT should only be supported at full level of compliance with the SQL-92 standard. So, some DBMSs instead of the phrase
When you often come across any technology, programming language, or standard, a certain picture of their capabilities and the boundaries within which they are used are formed. This can go on for quite a long time until the eye catches examples that expand the hardened horizons of knowledge. Today, I would like to talk about such examples and demonstrate them for the SQL language. Interesting and rare designs, forgotten expressions, strange techniques await you in this article. Anyone interested, welcome to cat.Nuances
I am often asked, who is this article for? But, believe me, it’s not always easy to give an answer: on the one hand, there are ninja developers who are difficult to surprise with anything, and on the other, young padawans. But I can say one thing for sure - for a reader who is interested in SQL, who is able to complement his rich picture with small but very interesting details. This article will not contain kilometer-long pages of sql queries, a maximum of 1 or 2 lines and only what is rare in my opinion. But since I want to be completely frank, if you are no stranger to sql, the article will seem a bit boring. All examples in the article, with the exception of the first and fourth, can be attributed to the SQL-92 standard.Data
In order to make our life easier, I have put up a simple data plate on which certain points will be tested and for the sake of brevity, I will give the result of the experiment on them. I check all queries on PostgreSql.Scripts and data table
CREATE TABLE goods(id bigint NOT NULL, name character varying(127) NOT NULL, description character varying(255) NOT NULL, price numeric(16,2) NOT NULL, articul character varying(20) NOT NULL, act_time timestamp NOT NULL , availability boolean NOT NULL, CONSTRAINT pk_goods PRIMARY KEY (id)); INSERT INTO goods (id, name, description, price, articul, act_time, availability) VALUES (1, "Slippers", "Soft", 100.00, "TR-75", (ts "2017-01-01 01:01: 01.01"), TRUE); INSERT INTO goods (id, name, description, price, articul, act_time, availability) VALUES (2, "Pillow", "White", 200.00, "PR-75", (ts "2017-01-02 02:02: 02.02"), TRUE); INSERT INTO goods (id, name, description, price, articul, act_time, availability) VALUES (3, "Blanket", "Down", 300.00, "ZR-75", (ts "2017-01-03 03:03: 03.03"), TRUE); INSERT INTO goods (id, name, description, price, articul, act_time, availability) VALUES (4, "Pillowcase", "Grey", 400.00, "AR-75", (ts "2017-01-04 04:04: 04.04"), FALSE); INSERT INTO goods (id, name, description, price, articul, act_time, availability) VALUES (5, "Sheet", "Silk", 500.00, "BR-75", (ts "2017-01-05 05:05: 05.05"), FALSE);
Requests
1. Double quotes
And the first thing I have is a simple question: Could you give an example of a sql query using double quotes? Yes, not with singles, doubles?Example with double quotes
SELECT name "Product name" FROM goods
I was very surprised when I saw this for the first time. If you try to change double quotes to single quotes, the result will be completely other!
This may not seem like a very useful example for real development. For me this is not the case. Now I actively use it in all my SQL templates. The point is simple: when you return after half a year to an sql query of 40 columns, oh how their “our” name saves you. Despite the fact that I did not mention about SQL-92, in the latest edition there is a mention of double quotes.
2. Pseudo table. SQL-92
It’s a little inaccurate from the point of view of terminology, but the essence is simple - the table resulting from a subquery in the FROM section. Perhaps the most famous fact in this articlePseudo table
SELECT mock.nickname "Nickname", (CASE WHEN mock.huff THEN "Yes" ELSE "No" END) "Offended?" FROM (SELECT name AS nickname, availability AS huff FROM goods) mock
In our example, the mock is a pseudo table (sometimes called a virtual table). Naturally, they are not intended at all to distort the true meaning. An example is this.
3. Data block constructor. SQL-92
It sounds scary, simply because I haven't found a good translation or interpretation. And as always, it’s easier to explain with an example:Data block constructor example
SELECT name "Product name", price "Price" FROM (VALUES ("Slippers", 100.00), ("Pillow", 200.00)) AS goods(name, price)
| Product name | Price |
| Slippers | 100.00 |
| Pillow | 200.00 |
In section FROM keyword used VALUES, followed by data in parentheses, line by line. The point is that we don’t select data from any table at all, but simply create it on the fly, “call” it a table, name the columns, and then use it at our own discretion. This thing turned out to be extremely useful when testing different sql query cases, when there is no data for some tables (in your local database), and writing insert is too lazy or sometimes very difficult, due to the relatedness of the tables and restrictions.
4. Time, Date and Time-and-Date
Probably everyone has encountered in requests the need to specify time, date or date-and-time. Many DBMSs support the literals t, d, and ts, respectively, for working with these types. But it’s easier to explain with an example: For the literals d and t, everything is similar.I apologize to the reader for misleading me, but everything that is said in paragraph 4 does not relate to the SQL language, but relates to the capabilities of preprocessing queries in JDBC.
5. Denial. SQL-92
We all know about the operator NOT, but very often they forget that it can be applied both to a group of predicates and to a single column:6. Comparison of data blocks. SQL-92
Once again I apologize for the terminology. This is one of my favorite examplesExample of comparing data blocks
SELECT * FROM goods WHERE (name, price, availability) = ("Pillowcase", 400.00, FALSE) -- or its equivalent SELECT * FROM goods WHERE name = "Pillowcase" AND price = 400.00 AND availability = FALSE
As can be seen from the example, comparing data blocks is similar to comparing element-by-element meaning_ 1 _block_1 = value_ 1 _block_2, value_ 2 _block_1 = value_ 2 _block_2, value_ 3 _block_1 = value_ 3 _block_2 using AND between them.
7. Comparison operators with modifiers ANY, SOME or ALL. SQL-92
This is where some clarification is required. But as always, first an example What does it mean ALL in this case? And it means that the selection condition is satisfied only by those rows whose identifiers (in our case these are 4 and 5) are greater any from the found values in the subquery (1, 2 and 3). 4 is greater than 1 and than 2 and than 3. 5 is the same. What happens if we replace ALL on ANY?What does it mean ANY in this case? What it means is that the selection condition is satisfied only by those rows whose identifiers (in our case these are 2, 3, 4 and 5) are greater at least one from the found values in the subquery (1, 2 and 3). For myself I associated ALL With AND, A ANY With OR. SOME And ANY analogues to each other.
8. Operators for working with/under requests. SQL-92
It is well known that you can combine 2 queries with each other using the operators UNION or UNION ALL. This is used often. But there are 2 more operators EXCEPT And INTERSECT.Example with EXCEPT
Actually, the data from the second set is excluded from the first set of values.
Actually, the intersection of the first set of values and the second set occurs.
That's all, thank you for your attention.
Editorial
N1. Thanks to streetflush for the constructive criticism. Contributed an article with information about what is a language standard and what is not.N2. Point 4 has been corrected to clarify that ts/d/t is not part of the SQL language. Thank you for your attention Melkij.
The lesson will cover the topic of using the operations of union, intersection and difference queries. Examples of how it is used SQL query Union, Exists, and the use of the SOME, ANY and All keywords. String functions covered
You can perform the operations of union, difference, and Cartesian product on a set. The same operations can be used in sql queries (perform operations with queries).
A special word is used to combine several queries UNION.
Syntax:
< запрос 1 >UNION[ALL]< запрос 2 > <запрос 1>UNION<запрос 2>
The Union SQL query is used to combine the output rows of each query into a single result set.
If used parameter ALL, then all duplicate output lines are saved. If the parameter is missing, then only unique rows remain in the result set.
You can combine any number of queries together.
Using the UNION operator requires several conditions to be met:
- the number of output columns of each query must be the same;
- the output columns of each query must be comparable to each other by data type (in order of priority);
- the resulting set uses the column names specified in the first query;
- ORDER BY can only be used at the end of a compound query because it applies to the result of the join.
Example: Display prices for computers and laptops, as well as their numbers (i.e., unload from two different tables in one query)
✍ Solution:
| 1 2 3 4 5 6 | SELECT `Number` , `Price` FROM pc UNION SELECT `Number` , `Price` FROM notebook ORDER BY `Price` |
SELECT `Number` , `Price` FROM pc UNION SELECT `Number` , `Price` FROM notebook ORDER BY `Price`
Result:
Let's look at a more complex example with an inner join:
Example: Find product type, number and price of computers and laptops
✍ Solution:
| 1 2 3 4 5 6 7 8 | SELECT product. `Type` , pc. `Number` , `Price` FROM pc INNER JOIN product ON pc. `Number` = product. `Number` UNION SELECT product. `Type` , notebook. `Number` , `Price` FROM notebook INNER JOIN product ON notebook. `Number` = product. `Number` ORDER BY `Price` |
SELECT product.`Type` , pc.`Number` , `Price` FROM pc INNER JOIN product ON pc.`Number` = product.`Number` UNION SELECT product.`Type` , notebook.`Number` , `Price` FROM notebook INNER JOIN product ON notebook.`Number` = product.`Number` ORDER BY `Price`
Result: 
SQL Union 1. Find manufacturer, part number and price of all laptops and printers
SQL Union 2. Find numbers and prices of all products released by the manufacturer Russia
SQL Existence Predicate EXISTS
SQL has facilities for performing intersection and difference operations on queries—the INTERSECT clause (intersection) and the EXCEPT clause (difference). These clauses work in a similar way to how UNION works: the result set includes only those rows that are present in both queries - INTERSECT , or only those rows of the first query that are missing in the second - EXCEPT . But the trouble is that many DBMSs do not support these proposals. But there is a way out - using the EXISTS predicate.
The EXISTS predicate evaluates to TRUE if the subquery returns at least some rows, otherwise EXISTS evaluates to FALSE. There is also the NOT EXISTS predicate, which does the opposite.
Typically EXISTS is used in dependent subqueries (for example, IN).
EXISTS(table subquery)
Example: Find computer manufacturers who also produce laptops
✍ Solution:
SELECT DISTINCT Manufacturer FROM product AS pc_product WHERE Type = "Computer" AND EXISTS (SELECT Manufacturer FROM product WHERE Type = "Laptop" AND Manufacturer = pc_product.Manufacturer)
Result: 
Find those computer manufacturers that do not make printers
SQL SOME Keywords | ANY and ALL
The keywords SOME and ANY are synonymous, so you can use either of them in your query. The result of such a query will be one column of values.
Syntax:
< выражение>< оператор сравнения>SOME | ANY (< подзапрос> ) <выражение><оператор сравнения>SOME | ANY (<подзапрос>)
If for any value X returned from a subquery, the result of the " " operation returns TRUE , then the ANY predicate also evaluates to TRUE .
Example: Find computer suppliers whose numbers are not on sale (i.e. not in the pc table)
✍ Solution:
Table source data:
Result: 
In the example, the predicate Number = ANY(SELECT Number FROM pc) will return the value TRUE when the Number from the main query is found in the list of Numbers of table pc (returned by the subquery). Additionally, NOT is used. The result set will consist of one column - Manufacturer. To prevent one manufacturer from being displayed several times, the service word DISTINCT has been introduced.
Now let's look at using the ALL keyword:
Example: Find numbers and prices of laptops that cost more than any computer
✍ Solution:
Important: It is worth noting that in general, a query with ANY returns a set of values. Therefore, using a subquery in a WHERE clause without the EXISTS , IN , ALL , and ANY operators, which produce a Boolean value, may result in a query runtime error
Example: Find numbers and prices of computers whose cost exceeds the minimum cost of laptops
✍ Solution:
This query is correct because the scalar expression Price is compared with a subquery that returns a single value
Functions for working with strings in SQL
The LEFT function cuts the number of characters specified by the second argument from the left of a string:
LEFT (<строка>,<число>)
The RIGHT function returns the specified number of characters to the right from a string expression:
RIGHT(<строка>,<число>)
Example: Print the first letters of the names of all manufacturers
✍ Solution:
SELECT DISTINCT LEFT(`Manufacturer` , 1) FROM `product`
Result: 
Example: Print manufacturer names that begin and end with the same letter
✍ Solution:
SQL Replace function
Syntax:
SELECT `name` , REPLACE(`name` , "a", "aa") FROM `teachers`
There is only one important rule to remember when using the EXCEPT statement.
The order, number, and data types of columns must be the same in all queries.
According to the ANSI standard, the UNION and EXCEPT set operators have the same precedence, but the INTERSECT operator is executed before other set operators. We recommend explicitly controlling operator precedence using parentheses. This is generally a very good practice.
According to the ANSI standard, you can only use one ORDER BY clause in a query. Insert it at the very end of the last SELECT statement. To avoid ambiguity in naming columns and tables, be sure to assign the same alias to all matching table columns. For example:
SELECT au_lname AS "lastname", au_fname AS "firstname" FROM authors EXCEPT SELECT emp_lname AS "lastname", emp_fname AS "firstname" FROM employees ORDER BY lastname, firstname;
Additionally, because each column list can specify columns with correspondingly compatible data types, different RDBMS platforms may have different options for dealing with columns of different lengths. For example, if the au_lname column from the first query in the previous example is significantly longer than the emp_lname column from the second query, then different platforms may have different rules for determining the length of the final result. But generally speaking, platforms will choose a longer (and less restrictive) size for the result.
Each RDBMS may have its own rules for using a column name if the names in the column lists are different. In general, the column names of the first query are used.
The data types do not have to be identical, but they must be compatible. For example, the types CHAR and VARCHAR are compatible. By default, the result set in each column will be the size corresponding to the largest type at each particular position. For example, a query that retrieves data from columns containing values of type VARCHAR(IO) and VARCHAR(15) would use the VARCHAR(15) type and size.
Neither platform supports the CORRESPONDING )) EXCEPT clause
(SELECT statemenr.2 | VALUES (expressionl, expression2 [, ...])) EXCEPT
Allows you to specify one or more manually specified columns that are included in the final result set. (This is called a row constructor.) The VALUES clause must specify exactly as many columns as the EXCEPT statement queries. Although the EXCEPT DISTINCT statement is not supported, the functional equivalent is EXCEPT. The CORRESPONDING clause is not supported. Additionally, the data types LONG VARCHAR, LONG VARGRAPHIC, BLOB, CLOB, DBCLOB, DATALINK, and structure types are not used in the EXCEPT clause, but they can be used in the EXCEPT ALL clause.
If the result set has a column that has the same name in all SELECT statements, then that name is used as the final name for the column returned by the statement. If a given column is named differently in different SELECT statements, then you must rename the column in all queries using the same AS alias clause in all of them.
If a single query uses multiple operators to work with data sets, the one enclosed in parentheses is executed first. After this, the order of execution will be from left to right. However, all INTERSECT statements are executed before the UNION and EXCEPT statements. For example:
SELECT empno FROM employee WHERE workdept LIKE "E%" EXCEPT SELECT empno FROM emp_act WHERE projno IN (TF1000", TF2000", -AD3110")) UNION VALUES ("AA0001"), ("AB0002"), ("AC0003") ;
In the example above, the IDs of all employees working in the department that starts with "E" are retrieved from the employee table, then the IDs of those employed in projects IF1000, IF200, and AD3110 are removed from the employee accounts table (emp_act). Finally, three additional IDs are added - AA0001, AB0002 and AC0003 using the UNION set operator.
MySQL
MySQL does not support the EXCEPT operator. Alternatively, you can use the NOT IN or NOT EXISTS operators.
In this tutorial you will learn how to use EXCEPT operator in SQL Server(Transact-SQL) with syntax and examples.
Description
SQL Server EXCEPT statement(Transact-SQL) is used to return all rows in the first SELECT statement that are not returned by the second SELECT statement. Each SELECT statement will define a data set. The EXCEPT operator will retrieve all records from the first data set and then remove all records from the second data set from the results.
Except Query
Explanation: The EXCEPT query will return records in a gray shaded area. These are records that exist in SELECT 1 and not in SELECT 2.
Each SELECT statement in an EXCEPT query must have the same number of fields in result sets with similar data types.
Syntax
EXCEPT statement syntax in SQL Server (Transact-SQL):
Parameters or Arguments
expressions are the columns or calculations you want to compare between two SELECT statements. They do not have to be the same fields in each SELECT statement, but the corresponding columns must be of similar data types.
tables - tables from which you want to get records. There must be at least one table listed in the FROM clause.
WHERE conditions - optional. Conditions that must be met for the selected records.
Note
- Both SELECT statements must have the same number of expressions.
- The corresponding columns in each SELECT statement must have similar data types.
- The EXCEPT statement returns all records from the first SELECT statement that are not in the second SELECT statement.
- The EXCEPT operator in SQL Server is equivalent to the MINUS operator in Oracle.
Single expression example
Let's look at an example of an EXCEPT statement in SQL Server (Transact-SQL) that returns a single field with the same data type.
For example:
Transact-SQL
SELECT product_id FROM products EXCEPT SELECT product_id FROM inventory;
SELECT product_id FROM products SELECT product_id FROM inventory ; |
This EXCEPT statement example returns all product_id values that are in the products table and not in the inventory table. This means that if a product_id value exists in the products table and also exists in the inventory table, the product_id value will not appear in the results of the EXCEPT query.
Example with multiple expressions
Next, let's look at an example EXCEPT query in SQL Server (Transact-SQL) that returns more than one column.
For example:
Transact-SQL
In this example, the EXCEPT query returns records in the contacts table with the name contact_id , last_name , and first_name , which does not match the value employee_id , last_name , and first_name in the employees table.