use sql to query the database, and if there is no data in the field, set the data in the field to a certain value? How to write such sql ?
use sql to query the database, and if there is no data in the field, set the data in the field to a certain value? How to write such sql ?
take it apart and do it, it is impossible to do it with a single SELECT;
add a sub-statement, and the IF function docks UPDATE.
Old Daili has only these two methods for the time being.
1:
SELECT RegName,
RegEmail,
RegPhone,
RegOrg,
RegCountry,
DateReg,
ISNULL(Website,'no website') AS WebSite
FROM RegTakePart
WHERE Reject IS NULL
2:
SELECT RegName,
RegEmail,
RegPhone,
RegOrg,
RegCountry,
DateReg,
COALESCE(Website,'no website') AS WebSite
FROM RegTakePart
WHERE Reject IS NULL
mysql> select * from test2;
+----+------+
| id | id2 |
+----+------+
| -1 | -1 |
| 0 | NULL |
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 5 | 5 |
+----+------+
6 rows in set (0.00 sec)
mysql> select id,ifnull(id2,"") from test2;
+----+-------------------+
| id | ifnull(id2,"") |
+----+-------------------+
| -1 | -1 |
| 0 | |
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 5 | 5 |
+----+-------------------+
6 rows in set (0.00 sec)I wonder if I can help you
ifnull (columnValue,defaultValue)
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