InterSect SQL examples. Operator for Intersect Data Sets. An example with one expression

SQL provides two ways to combine tables:

specifying the connected tables (including subqueries) in the FROM phrase of the SELECT statement. First, the connection of the tables is performed, and only the conditions specified by the phrase of the group by aggregation, the ordering of the data, etc., are used to the resulting set.
defining the integration of the resulting sets obtained during the processing of the SELECT statement. In this case, the two SELECT operators are connected by the phrase Union, Intersect., Except or correSponding.

Union Union

Phrase Union Combines the results of two requests on the following rules:

Standard does not impose any restrictions on streaming rows in the resulting set. So, some DBMS first display the result of the first request, and then the result of the second query. The Oracle DBMS automatically sorts the records on the first specified column even if the index is not created for it.

In order to explicitly specify the desired sorting order, the ORDER BY phrase should be used. In this case, you can use both the name of the column and its number (Fig. 4.3).

Fig. 4.3.

Phrase Union All performs the union of two subqueries in the same way as the Union phrase with the following exceptions:

the coinciding lines are not removed from the resulting resulting set;
combined queries are displayed in the resulting set sequentially without ordering.

When combining more than two requests to change the order of the merge operation, you can use brackets (Fig. 4.4).

Fig. 4.4.

InterSect-association

Phrase Intersect. Allows you to select only those lines that are present in each united resulting set. In fig. 4.5 An example of combining requests as intersecting sets is given.

Fig. 4.5.

Except Union

Phrase Except Allows you to select only those lines that are present in the first combined resulting set, but are absent in the second result set.

Phrases Intersect. and Except Must be supported only with the full compliance level of the SQL-92 standard. So, some DBMS instead of the phrase

There is only one important rule of using the Except instruction that you need to remember.

Order, quantity and types of data columns must be the same type in all requests.

According to the ANSI standard, operators with Union and Except sets have the same priority, but the InterSect statement is performed before other operators for sets. We recommend explicitly to manage the priority of operators using brackets. This is generally very good practice.

According to the ANSI standard, only one ORDER BY offer can be used. Insert it to the easiest of the latest SELECT statement. To avoid ambiguity in specifying columns and tables, be sure to assign the same alias to all the corresponding to each other columns of the tables. 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;

In addition, since in each list of columns, columns can be indicated with respectively compatible data types, various options for working with columns of different lengths may occur on different platforms of SURBD. For example, if the AU_LNAME column from the first request in the previous example is much longer than the EMP_LNAME column from the second request, then different platforms can apply different rules for determining the length of the final result. But, generally speaking, the platforms will choose the result of a longer (and less limited) size.

Each SURGD can apply his own rules for using the column name if the names in the columns lists differ. In the general case, the names of the first request columns are used.

Types of data should not be identical, but they must be compatible. For example, CHAR and VARCHAR types are compatible. By default, the resulting set in each column will be used the size corresponding to the largest type in each specific position. For example, a request that extracts data from columns containing values \u200b\u200bof type VARCHAR (IO) and VARCHAR (15) will use the type and size of VARCHAR (15).

None of the platforms support the Corresponding offer)) Except

(SELECT STATEMENR.2 | VALUES (Expressionl, Expression2 [, ...])) Except

Allows you to specify one or more manually defined columns, which are included in the final result set. (This is called the row designer.) In the value of Values, there must be exactly so many columns as they are specified in the Except operator queries. Although the Except Distinct instruction is not supported, the functional equivalent is EXCEPT. Corresponding Offer is not supported. Also, Long Varchar, Long Vargraphic, Blob, Clob, DBClob, DataLink, DataLink and Structural Types are not used in the Except offer, but they can be used in Except All.

If the resulting set of data is a column that has the same name in all SELECT instructions, then this name is used as a final name for the column returned by the instruction. If this column is called differently in different SELECT instructions, then you must rename the column in all requests using the same as a pseudonym in all of them.

If several operators are used in one query to work with data sets, then the first one that is enclosed in brackets is performed. After that, the order of execution will be left to right. Nevertheless, all interSect statements are performed before UNION and EXCEPT operators. For example:

SELECT EMPNO from Employee Where WorkDept Like "E%" Except Select Empno from Emp_Act Where Projno in (TF1000 ", TF2000", -Ad3110 ")) Union Values \u200b\u200b(" AA0001 "), (" AB0002 "), (" AC0003 ") ;

In the above example from the Employee table, identifiers (ID) of all employees operating in the Department, the name of which begins with "E", then the ID of those engaged in the IF1000, IF200 projects and AD3110 are excluded from the Emp_Act Accounting Table (EMP_ACT) . And finally, three additional IDs are added - AA0001, AB0002 and AC0003 using the operator of the Union sets.

Mysql

In MySQL, the Except statement is not supported. Alternatively, you can use NOT IN operations or Not EXISTS.

InterSect operator extracts identical lines from the resulting sets of one or more requests. In some respects, the InterSect statement is very reminded by Inner Join.

Intersect refers to the class class to work with data sets (Set Operator). Other such operators include Except and Union. All operators for data sets are used to simultaneously manipulate the resulting sets of two or more requests, from here and their name.

SQL2003 syntax

Technical restrictions on the number of requests in the interSect statement does not exist. The general syntax is next.

Intersect.

] InterSect.

Keywords

Duplicate lines from all result sets are included.

Distinct.

Duplicate strings are removed from all the resulting sets before comparing the InterSect operator. Columns with empty (NULL) values \u200b\u200bare considered duplicate. If neither the ALL keyword nor the Distinct is indicated, then the default is Distinct.

Corresponding

It is indicated that only those columns that have one name in both requests will be returned, even if the symbol (*) is used in both requests.

It is indicated that only these columns will be returned, even if requests detect other columns with the corresponding names. This proposal should be used with the keyword Corresponding.

General rules

There is only one important rule that you want to remember when working with the interSect operator.

The order and number of columns in all requests should be equally. The data types of the corresponding columns must also be compatible.

For example, CHAR and VARCHAR types are compatible. By default, the resulting set in each column will be used the size corresponding to the largest type in each specific position.

None of the platforms support the Corresponding offer.

According to the ANSI standard, the InterSect statement has a higher priority compared to other operators to work with sets, although on different platforms the priority of such operators is processed differently. You can explicitly manage the priority of operators using brackets. Otherwise, the DBMS can perform them in order from left to right or from the first to last.

On platforms that do not support the InterSect statement, you can replace it with a subquery Full Join.

Select a.au_lname as "LastName", a.au_fname as "firstName" from authors as a intersect select e.emp_lname as "lastname", e.Emp_fname as "firstname" from Employees as e Order by Lastname, FirstName;

Since the column data types in different requests in the InterSect operator may be compatible, various options for working with columns of different lengths may occur on different SURBD platforms. For example, if the Aujname column from the first request in the previous example is much longer than the EmpJName column from the second query, then different platforms can apply different rules for determining the end result. But, generally speaking, the platforms will choose the result of a longer (and less limited) size.

Each SURGD can apply his own rules for using the column name if the names in the columns lists differ. The names of the first request columns are usually used.

DB2.

The DB2 platform supports the intersect keywords and intersect ALSI Standard plus an additional value of Values.

(Instruction._select_7 | Values \u200b\u200b(expressing7 [, ...])) intersect

] (instruction_scj_2 | values \u200b\u200b(expressing 2 [, ...])) intersect

Although INTERSECT DISTINCT statement is not supported, the functional equivalent is interSect. Corresponding Offer is not supported.

In addition, Long Varchar, Long Vargraphic, Blob, Clob, DBClob, DataLink and Structural Types are not used in the InterSect Offer, but you can use Intersect All.

If the resulting set of data is a column that has the same name in all SELECT instructions, then this name is used as a final name for the column returned by the instruction. If different names are used in queries for column, the DB2 platform will generate a new name for the resulting column. After that, it becomes unsuitable for use in ORDER BY and FOR UPDATE offers.

If several operators are used in one query to work with data sets, then the first one that is enclosed in brackets is performed. After that, the order of execution will be left to right. However, all interSect statements are performed to Union and Except statements, for example:

Select Empno from Employee Where WorkDept Like "E%" InterSect (Select Empno from Emp_Act Where Projno in ("IF1000", "IF2000", "AD3110") Union Values \u200b\u200b("AA0001"), ("AB0002"), ("AC0003 "))

In the example above, the identifiers (ID) of all employees operating in the Department, whose name begins with "E" is retrieved from the Employee table. However, identifiers are retrieved only if they also exist in the employee accounts table with the name EMP_ACT and participate in the IF1000, IF200 and AD3110 projects.

In this tutorial, you will learn how to use except operator in SQL Server (TRANSACT-SQL) with syntax and examples.

Description

Except SQL Server Operator (Transact-SQL) Used to return all rows in the first SELECT statement, which are not returned by the second SELECT statement. Each SELECT statement will define a data set. The Except operator will extract all records from the first dataset, and then delete all records from the second dataset from the results.

EXCEPT request

Explanation: Except request will return recording in a gray shaded area. These are the 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 the results sets with similar data types.

Syntax

Except operator syntax in SQL Server (Transact-SQL):

Parameters or arguments

expressions - columns or calculations that you want to compare between two SELECT operators. They should not be the same fields in each of the SELECT statements, but the corresponding columns should be with similar data types.
tables - Tables from which you want to receive records. There must be at least one table listed in the FROM sentence.
Where Conditions - optional. Conditions that must be completed for selected entries.

Note

In both SELECT operators, there must be the same number of expressions.
The corresponding columns in each of the SELECT statements should have similar data types.
Except operator returns all records from the first SELECT statement that is not included in the second SELECT statement.
Except operator in SQL Server is equivalent to the MINUS operator in Oracle.

An example with one expression

Let's consider an example of an Except operator in SQL Server (Transact-SQL), which returns one 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 example of an Except operator returns all the Product_ID values \u200b\u200bthat are in the Products table, and not in the Inventory table. This means that if the product_id value exists in the Products table and also exists in the Inventory table, the product_id value will not be displayed in the Except query results.

Example with multiple expressions

Then let's consider an example of an Except query in SQL Server (Transact-SQL), which returns more than one column.
For example:

Transact-sql.

In this example, the Except request returns the records in the Contacts table with the name Contact_ID, Last_Name and First_Name, which does not match the employee_id value, last_name and first_name in the EmployeEes table.