# Assigning Expressions to Variables

You can reference system variables, [user-defined variables](https://docs.singlestore.com/db/v9.1/reference/sql-reference/user-defined-variables.md), literals, or any combination of these using built-ins like `CONCAT`, and  the `SELECT` statement as a variant of complex expressions.

Example:

```sql
SET sql_mode = CONCAT(@@sql_mode, _utf8', ONLY_FULL_GROUP_BY');
```

You can connect to a CA, set session variables, and then use  `SET GLOBAL` or `SET AGGREGATOR` referencing these variables. Values are evaluated on the CA and then forwarded to the MA.

You can set system variables using complex expressions inside stored procedures.

Example:

```sql
CREATE OR REPLACE PROCEDURE db.fff() AS
    BEGIN
        SET wait_timeout = 30001 + (SELECT b FROM db.t WHERE a = 3);     
        ECHO SELECT @@session.wait_timeout;
    END;    
```

There is a limitation that applies to all DDL statements inside stored procedures. They  cannot access the stored procedure’s arguments and local variables. The workaround is to use `EXECUTE IMMEDIATE`.

Example:

```sql
CREATE OR REPLACE PROCEDURE db.fff(arg int) AS 
    DECLARE q text; 
    BEGIN   
        q = CONCAT('SET wait_timeout = 30001 + ', arg, ' + (SELECT b FROM db.t WHERE a = 3)');   
        EXECUTE IMMEDIATE q;   
        ECHO SELECT @@session.wait_timeout; 
    END;                    
```

## Examples Using [SET GLOBAL](https://docs.singlestore.com/db/v9.1/reference/sql-reference/operational-commands/set-global.md) and [SET SESSION](https://docs.singlestore.com/db/v9.1/reference/sql-reference/operational-commands/set-and-set-session.md)

Example 1:

```sql
SET @new_mode = 'ANSI_QUOTES,';
SET @@GLOBAL.sql_mode = CONCAT(@new_mode, 'ONLY_FULL_GROUP_BY');
SELECT @@GLOBAL.sql_mode;
```

Example 2:

```sql
SET GLOBAL exporter_ssl_capath=`what's "going" on`;
SELECT @@GLOBAL.exporter_ssl_capath;
```

Example 3:

```sql
SET SESSION net_read_timeout = (SELECT COUNT(*) FROM db.t) * 400;
SELECT @@SESSION.net_read_timeout;
```

Example 4:

```sql
SET SESSION sql_mode=(select concat(@@sql_mode,',ANSI_QUOTES'));
SELECT @@sql_mode;
```

Example 5:

```sql
SET SESSION inlist_precision_limit = 2000;
SET @cvar = 200;
SET GLOBAL inlist_precision_limit = @@inlist_precision_limit + @cvar;
SELECT @@inlist_precision_limit;
SELECT @@GLOBAL.inlist_precision_limit;
```

***

Modified at: April 25, 2025

Source: [/db/v9.1/reference/configuration-reference/engine-variables/assigning-expressions-to-variables/](https://docs.singlestore.com/db/v9.1/reference/configuration-reference/engine-variables/assigning-expressions-to-variables/)

(An index of the documentation is available at /llms.txt)