How to declare a variable in MySQL?

user_665557 0
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How to declare a variable in mysql, so that my second query can use it?

I would like to write something like:

SET start = 1;
SET finish = 10;

SELECT * FROM places WHERE place BETWEEN start AND finish;
mysql sql
7 Answers

Different types of variable:

  • local variables (which are not prefixed by @) are strongly typed and scoped to the stored program block in which they are declared. Note that, as documented under DECLARE Syntax:

DECLARE is permitted only inside a BEGIN ... END compound statement and must be at its start, before any other statements.

  • User variables (which are prefixed by @) are loosely typed and scoped to the session. Note that they neither need nor can be declared—just use them directly.

Therefore, if you are defining a stored program and actually do want a "local variable", you will need to drop the @ character and ensure that your DECLARE statement is at the start of your program block. Otherwise, to use a "user variable", drop the DECLARE statement.

Furthermore, you will either need to surround your query in parentheses in order to execute it as a subquery:

SET @countTotal = (SELECT COUNT(*) FROM nGrams);

Or else, you could use SELECT ... INTO:

SELECT COUNT(*) INTO @countTotal FROM nGrams;

user_98264530

  • Declare: SET @a = 1;

  • Usage: INSERT INTO `t` (`c`) VALUES (@a);

user_47184340

For any person using @variable in concat_ws function to get concatenated values, don't forget to reinitialize it with empty value. Otherwise it can use old value for same session.

Set @Ids = '';

select 
  @Ids := concat_ws(',',@Ids,tbl.Id),
  tbl.Col1,
  ...
from mytable tbl;
user_36669150

SET Value

 declare @Regione int;   
 set @Regione=(select  id from users
 where id=1) ;
 select @Regione ;
user_66019390
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