Question

I have an alias in the select like this:

SELECT
    CASE ....
    WHEN 1 THEN somefield * -10
    WHEN 0 THEN somefield * 10
    END as myAlias
FROM
    ....

the problem is that at the first record that mysql seeks, it marks the “myAlias” as UNSIGNED
but in some next record the same alias produces a SIGNED integer, then I have the error:

BIGINT UNSIGNED value is out of range in....

so, how to tell mysql before it does any operation that “myAlias” is a SIGNED INTEGER?

thanks!

edit:

I’ve tried

SELECT
    CAST(CASE ....
    WHEN 1 THEN somefield * -10
    WHEN 0 THEN somefield * 10
    END AS SIGNED) as myAlias
FROM
    ....

without success!

Answer 1

I assume that the field in your table is declared as UNSIGNED INTEGER. In that case, you have to type cast the field in the THEN clause of the CASE expression. Below example illustrates a sample.

Create and insert script:

CREATE TABLE mytable
(
     numberfield INTEGER UNSIGNED
   , bitfield BIT
);

INSERT INTO mytable (numberfield, bitfield) VALUES
  (134, 1),
  (673, 0),
  (855, 1),
  (133, 0),
  (778, 1),
  (234, 0);

Type casting the field in THEN clause: SQL Fiddle Demo

SELECT
    CASE bitfield
        WHEN 1 THEN CAST(numberfield AS SIGNED) * -10
        WHEN 0 THEN CAST(numberfield AS SIGNED) * 10
    END as myAlias
FROM mytable

Output:

MYALIAS
-------
-1340
6730
-8550
1330
-7780
2340

Alternative way to write the above query: SQL Fiddle Demo

SELECT
    CAST(numberfield AS SIGNED) * 
    (
        CASE bitfield
            WHEN 1 THEN -10
            WHEN 0 THEN 10
        END
    ) as myAlias
FROM mytable

Output:

MYALIAS
-------
-1340
6730
-8550
1330
-7780
2340

Without type casting the field: SQL Fiddle Demo

SELECT
    CASE bitfield
      WHEN 1 THEN numberfield * -10
      WHEN 0 THEN numberfield * 10
    END as myAlias
FROM mytable

Error:

Data truncation: BIGINT UNSIGNED value is out of range in ‘(db_5b3bb.mytable.numberfield * -(10))’: SELECT CASE bitfield WHEN 1 THEN numberfield * -10 WHEN 0 THEN numberfield * 10 END as myAlias FROM mytable