Sql-Exit CASE Statement when condition is met

Question

The following CASE statement updates BET1 , BET2 , BET3 and BET4 at the same time when ID=10 .

$S1=32
$sql="UPDATE TIMER-BOARD1 
set BET1= case when BET1 IS NULL THEN $S1 else BET1 end ,
    BET2= case when BET2 IS NULL THEN $S1 else BET2 end,
    BET3= case when BET3 IS NULL THEN $S1  else BET3 end,
    BET4= case when BET4 IS NULL THEN $S1 else BET4 end
WHERE ID = 10";

When I run the php page, I have BET1=32 , BET2=32 , BET3=32 , BET4=32 .

What I want is to have the script exit when it finds and fills the first null field.

Ie, starting with all BET1 , BET2 , BET3 , BET4 = NULL when ID =10 , I want when I run the php page, to update only BET1=32 . And when I run it again, to update BET2=32 , etc.

Something similar to the following:

    $S1=32
    $sql="UPDATE TIMER-BOARD1 
    set BET1= case when BET1 IS NULL THEN $S1 
( EXIT AND DON’T BOTHER ABOUT OTHER CASE      STATEMENTS) else BET1 end ,
       BET2= case when BET2 IS NULL THEN $S1 
(EXIT AND DON’T BOTHER ABOUT OTHER CASE STATEMENTS) else BET2 end,
    BET3= case when BET3 IS NULL THEN $S1 
(EXIT AND DON’T BOTHER ABOUT OTHER CASE STATEMENTS)   else BET3 end,
    BET4= case when BET4 IS NULL THEN $S1 
(EXIT AND DON’T BOTHER ABOUT OTHER CASE STATEMENTS) else BET4 end
    WHERE ID = 10";

RESULTS

Start values: ID=10 ,BET1=NULL, BET2=NULL, BET3=NULL, BET4=NULL.

Run the script 1ST time: ID=10, BET1=32, BET2 =NULL, BET3=NULL, BET4=NULL.

Run the script 2nd time: ID=10, BET1=32, BET2= 32, BET3=NULL, BET4 = NULL.

Run the script 3rd time: ID=10, BET1=32, BET2=32, BET3=32, BET4=NULL.

Run the script 4th time: ID=10, BET1=32, BET2=32, BET3=32, BET4=32.

Run the script 5th time or more: No null field, so no change.

How can I edit the script to perform the above function?

EDIT

@ InoS Heo

One final question if you have the time.

I have $S1=32 before running the sql. Suppose instead of 32 I have susan, which is of course a string.

How can your script be updated to accommodate strings like above?

$S1 =susan
UPDATE `TIMER-BOARD1`
set 
    ID = @UPDATED := 10,
    BET1 = case when BET1 IS NULL THEN @UPDATED:= susan else BET1 end,
    BET2 = case when @UPDATED = 10 AND BET2 IS NULL THEN @UPDATED:= susan else BET2     end,
…
    BET4 = case when @UPDATED = 10 AND BET4 IS NULL THEN @UPDATED:= susan else BET4 end
WHERE ID = 10;

Thanks.

Answer 1

You are looking for "UPDATE first NULL column" . I think this can be achieved using MySQL User Variable.

Could you try this?

Schema & data

DROP TABLE IF EXISTS `TIMER-BOARD1`;
CREATE TABLE `TIMER-BOARD1` (
  `ID` int(11) NOT NULL,
  `BET1` int(11) DEFAULT NULL,
  `BET2` int(11) DEFAULT NULL,
  `BET3` int(11) DEFAULT NULL,
  `BET4` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

DELETE FROM `TIMER-BOARD1`;
INSERT INTO `TIMER-BOARD1` VALUES (10, NULL, NULL, NULL, NULL),
    (10, 32, NULL, NULL, NULL), (10, 1, 2, NULL, NULL),
    (10, 1, 2, 3, NULL), (10, 1, 2, 3, 4);

Initial Data

SELECT * FROM `TIMER-BOARD1`;
+----+------+------+------+------+
| ID | BET1 | BET2 | BET3 | BET4 |
+----+------+------+------+------+
| 10 | NULL | NULL | NULL | NULL |
| 10 |   32 | NULL | NULL | NULL |
| 10 |    1 |    2 | NULL | NULL |
| 10 |    1 |    2 |    3 | NULL |
| 10 |    1 |    2 |    3 |    4 |
+----+------+------+------+------+

UPDATE

UPDATE `TIMER-BOARD1`
set 
    ID = @UPDATED := 10, -- user defined variable which keep track WHETHERE CHANGED OR NOT
    BET1 = case when BET1 IS NULL THEN @UPDATED:= 32 else BET1 end,
    BET2 = case when @UPDATED = 10 AND BET2 IS NULL THEN @UPDATED:=32 else BET2 end,
    BET3 = case when @UPDATED = 10 AND BET3 IS NULL THEN @UPDATED:=32 else BET3 end,
    BET4 = case when @UPDATED = 10 AND BET4 IS NULL THEN @UPDATED:=32 else BET4 end
WHERE ID = 10;

updated data

SELECT * FROM `TIMER-BOARD1`;
mysql> SELECT * FROM `TIMER-BOARD1`;
+----+------+------+------+------+
| ID | BET1 | BET2 | BET3 | BET4 |
+----+------+------+------+------+
| 10 |   32 | NULL | NULL | NULL |
| 10 |   32 |   32 | NULL | NULL |
| 10 |    1 |    2 |   32 | NULL |
| 10 |    1 |    2 |    3 |   32 |
| 10 |    1 |    2 |    3 |    4 |
+----+------+------+------+------+

Problem

Still has a problem when you want to UPDATE 10.

UPDATED

1. USING some string_column

I think you have two choices

1. using string column rather than ID column
   • pros : can be achieved using one UPDATE
   • cons : can't be used if there are no more string column
2. execute UPDATE for each rows
   • pros : can be used even if there are no more string column
   • cons : executes several UPDATE, Can't be used if there are no PK.

I wonder if you have some string column like string_col as follows.

Schema & Data

DROP TABLE IF EXISTS tab;

CREATE TABLE tab (
  `ID` int(11) NOT NULL,
  `BET1` VARCHAR(100) DEFAULT NULL,
  `BET2` VARCHAR(100) DEFAULT NULL,
  `BET3` VARCHAR(100) DEFAULT NULL,
  `BET4` VARCHAR(100) DEFAULT NULL,
  `string_col` VARCHAR(100) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

DELETE FROM tab;
INSERT INTO tab VALUES
    (10, NULL, NULL, NULL, NULL, 'A'),
    (10, 'Alice', NULL, NULL, NULL, 'B'),
    (10, 'Alice', 'Bob', NULL, NULL, 'C'),
    (10, 'Alice', 'Bob', 'Charlie', NULL, 'D'),
    (10, 'Alice', 'Bob', 'Charlie', 'Dave', 'E');

SELECT * FROM tab;
+----+-------+------+---------+------+------------+
| ID | BET1  | BET2 | BET3    | BET4 | string_col |
+----+-------+------+---------+------+------------+
| 10 | NULL  | NULL | NULL    | NULL | A          |
| 10 | Alice | NULL | NULL    | NULL | B          |
| 10 | Alice | Bob  | NULL    | NULL | C          |
| 10 | Alice | Bob  | Charlie | NULL | D          |
| 10 | Alice | Bob  | Charlie | Dave | E          |
+----+-------+------+---------+------+------------+

UPDATE

UPDATE tab
set 
    string_col = @ORIG_STRING_COL := (@UPDATED := string_col),
    BET1 = IF(BET1 IS NULL, @UPDATED := 'Susan', BET1),
    BET2 = IF(@UPDATED != 'Susan' AND BET2 IS NULL, @UPDATED := 'Susan', BET2),
    BET3 = IF(@UPDATED != 'Susan' AND BET3 IS NULL, @UPDATED := 'Susan', BET3),
    BET4 = IF(@UPDATED != 'Susan' AND BET4 IS NULL, @UPDATED := 'Susan', BET4),
    string_col = @ORIG_STRING_COL
WHERE ID = 10;

RESULT

SELECT * FROM tab;
+----+-------+-------+---------+-------+------------+
| ID | BET1  | BET2  | BET3    | BET4  | string_col |
+----+-------+-------+---------+-------+------------+
| 10 | Susan | NULL  | NULL    | NULL  | A          |
| 10 | Alice | Susan | NULL    | NULL  | B          |
| 10 | Alice | Bob   | Susan   | NULL  | C          |
| 10 | Alice | Bob   | Charlie | Susan | D          |
| 10 | Alice | Bob   | Charlie | Dave  | E          |
+----+-------+-------+---------+-------+------------+

2. execute one UPDATE for each record

With following pseudo code, you could achieve it.

$res = mysqli_query(SELECT pk_column FROM tab WHERE ID = 10);

while ($row = mysqli_fetch_assoc($res))
{
    $pk_col = $row['pk_column'];

    mysqli_query("SET @UPDATED := ''");

    mysqli_query("UPDATE tab
        SET 
            BET1 = IF(BET1 IS NULL, @UPDATED := 'Susan', BET1),
            BET2 = IF(@UPDATED = '' AND BET2 IS NULL, @UPDATED := 'Susan', BET2),
            BET3 = IF(@UPDATED = '' AND BET3 IS NULL, @UPDATED := 'Susan', BET3),
            BET4 = IF(@UPDATED = '' AND BET4 IS NULL, @UPDATED := 'Susan', BET4)
        WHERE pk_col = $pk_column
    ");

}

preceding code can be implemented client side or Stored procedure.

Answer 2

You can simply check that the other fields are already not null s:

UPDATE TIMER-BOARD1 
SET BET1= case when BET1 IS NULL THEN $S1 else BET1 end ,
    BET2= case when BET1 IS NOT NULL AND BET2 IS NULL THEN $S1 else BET2 end,
    BET3= case when BET1 IS NOT NULL AND BET2 IS NOT NULL AND BET3 IS NULL THEN $S1 else BET3 end,
    BET4= case when BET1 IS NOT NULL AND BET2 IS NOT NULL AND BET3 IS NOT NULL AND BET4 IS NULL THEN $S1 else BET4 end
WHERE ID = 10