# SELECT ... INTO User Defined Variable ## Syntax ```sql SELECT ... INTO @user_defined_variable [,...] ``` ## Remarks * Refer to user-defined variables as `@user_defined_variable`. * User-defined variables are case-insensitive, which means `@rollno` is the same as `@RollNo`. * These variables are session-specific; they expire once the session ends. Also, a session variable defined by a user cannot be viewed or referenced by another session. * The data type of a user-defined variable is inferred automatically. * The `INFORMATION_SCHEMA.USER_VARIABLES` table contains a list of all the user-defined variables. ## Limitations of User-Defined Variables * A user-defined variable must be assigned a value before it can be referenced in a query. * The `SELECT ... INTO` statement must return only a single row. * These variables cannot be used directly as an identifier or part of an identifier in a query, for example ``SELECT `@col_name` FROM table_name`` is not allowed. > **❗ Important**: An exception to this rule is a column defined as ``CREATE TABLE t (`@col_name` INT)``. In this case ``SELECT `@col_name` FROM t`` returns the value from the column. * These variables cannot be used in the `GROUP BY` or `ORDER BY` clause. * User-defined variables cannot be referenced in stored procedures, computed columns, user-defined functions, table-valued functions, or views. * If a query uses `@` in a `LOAD DATA` statement, SingleStore interprets it as a reference to a `LOAD DATA` assignment instead of a user-defined variable. ## Examples ## Example 1 The following example assigns a value to a user-defined variable, and then uses it in a `SELECT` statement. ```sql CREATE TABLE circle (Radius int); INSERT INTO circle VALUES(2),(3); ``` ```sql SELECT 3.14 INTO @pi; SELECT Radius, Radius*POW(@pi,2) AS "Area" FROM circle; ``` ```output +--------+---------+ | Radius | Area | +--------+---------+ | 2 | 19.7192 | | 3 | 29.5788 | +--------+---------+ ``` The data type of the user-defined variable was inferred automatically, based on its value. ```sql SELECT * FROM INFORMATION_SCHEMA.USER_VARIABLES; ``` ```output +---------------+----------------+-----------------------+ | VARIABLE_NAME | VARIABLE_VALUE | VARIABLE_TYPE | +---------------+----------------+-----------------------+ | pi | 3.14 | decimal(3,2) NOT NULL | +---------------+----------------+-----------------------+ ``` ## Example 2 The following example assigns a value to a user-defined variable using a `SELECT ... INTO` statement. ```sql CREATE TABLE udv_courses (course_code varchar(20), section_number int, number_students int); INSERT INTO udv_courses VALUES ("CS-101",1,20), ("CS-101",2,16), ("CS-101",3,22), ("CS-101",4,25), ("CS-101",5,22), ("CS-150",1,10), ("CS-150",2,16), ("CS-150",3,11), ("CS-150",4,17), ("CS-150",5,9), ("CS-201",1,14), ("CS-201",2,17), ("CS-301",1,7), ("CS-301",2,10); SELECT * FROM udv_courses ORDER BY course_code, section_number; ``` ```output +-------------+----------------+-----------------+ | course_code | section_number | number_students | +-------------+----------------+-----------------+ | CS-101 | 1 | 20 | | CS-101 | 2 | 16 | | CS-101 | 3 | 22 | | CS-101 | 4 | 25 | | CS-101 | 5 | 22 | | CS-150 | 1 | 10 | | CS-150 | 2 | 16 | | CS-150 | 3 | 11 | | CS-150 | 4 | 17 | | CS-150 | 5 | 9 | | CS-201 | 1 | 14 | | CS-201 | 2 | 17 | | CS-301 | 1 | 7 | | CS-301 | 2 | 10 | +-------------+----------------+-----------------+ ``` ```sql SELECT number_students FROM udv_courses WHERE course_code = 'CS-301' and section_number = 1 INTO @ns; SELECT @ns; ``` ```output +------+ | @ns | +------+ | 7 | +------+ ``` **Note**: The `SELECT ... INTO` statement must return only a single value. ## Example 3 The following example shows how using `@` in a `LOAD DATA` query is interpreted as a reference to `LOAD DATA` assignment, instead of a user-defined variable. ```sql SELECT 100 INTO @Views; SELECT @Views; ``` ```output +--------+ | @Views | +--------+ | 100 | +--------+ ``` ```sql SELECT * FROM allviews; ``` ```output +-------+---------+-------+ | State | Product | Views | +-------+---------+-------+ | NY | C | 15 | | CA | D | 20 | | CA | A | 60 | | CA | E | 50 | | CA | G | 10 | | NY | B | 20 | | NY | F | 40 | +-------+---------+-------+ ``` ``` cat /tmp/data.csv ``` ```output TX,H,25 TX,I,10 ``` ```sql LOAD DATA INFILE '/tmp/data.csv' INTO TABLE allviews FIELDS TERMINATED BY ',' (State,Product,@Views) SET Views = @Views + 10; SELECT * FROM allviews; ``` ```output +-------+---------+-------+ | State | Product | Views | +-------+---------+-------+ | NY | C | 15 | | CA | D | 20 | | TX | H | 35 | | TX | I | 20 | | CA | A | 60 | | CA | E | 50 | | CA | G | 10 | | NY | B | 20 | | NY | F | 40 | +-------+---------+-------+ ``` > **⚠️ Warning**: ## Implicit CollationWhen `character_set_server` is set to `utf8`, string literals with characters using 4-byte encoding are implicitly assigned binary collation and processed as a sequence of bytes rather than characters. This implicit conversion to binary collation causes string functions to return unexpected results. To avoid using implicit binary collation, either use explicit type casting or use database columns defined with the `utf8mb4` character set. For more information, refer to [Implicit Collation in Special Cases](https://docs.singlestore.com/db/v9.1/reference/sql-reference/character-encoding/special-cases.md). *** Modified at: March 8, 2024 Source: [/db/v9.1/reference/sql-reference/user-defined-variables/select-into-user-defined-variable/](https://docs.singlestore.com/db/v9.1/reference/sql-reference/user-defined-variables/select-into-user-defined-variable/) (An index of the documentation is available at /llms.txt)