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Check whether a field is empty or null in MySQL?
NULL and empty string ‘ ’ both aren’t similar in MySQL. To check the field is empty like ‘ ’or is null, you need to use the IS NULL property or something else. You can check all the conditions with CASE statement. The syntax is as follows:
SELECT *, CASE WHEN yourColumnName =’ ‘ THEN ‘yourMessage1’ WHEN yourColumnName IS NULL THEN ‘yourMessage2’ ELSE CONCAT(yourColumnName ,' is a Name') END AS anyVariableName FROM yourTableName;
To understand the above syntax, let us create a table. The query to create a table is as follows:
mysql> create table checkFieldDemo -> ( -> Id int NOT NULL AUTO_INCREMENT, -> Name varchar(10), -> PRIMARY KEY(Id) -> ); Query OK, 0 rows affected (0.64 sec)
Insert some records in the table using insert command. The query is as follows:
mysql> insert into checkFieldDemo(Name) values(NULL);
Query OK, 1 row affected (0.17 sec)
mysql> insert into checkFieldDemo(Name) values('John');
Query OK, 1 row affected (0.15 sec)
mysql> insert into checkFieldDemo(Name) values(NULL);
Query OK, 1 row affected (0.10 sec)
mysql> insert into checkFieldDemo(Name) values('');
Query OK, 1 row affected (0.51 sec)
mysql> insert into checkFieldDemo(Name) values('Carol');
Query OK, 1 row affected (0.14 sec)
mysql> insert into checkFieldDemo(Name) values('');
Query OK, 1 row affected (0.17 sec)
mysql> insert into checkFieldDemo(Name) values(NULL);
Query OK, 1 row affected (0.10 sec)Display all records from the table using select statement. The query is as follows:
mysql> select *from checkFieldDemo;
The following is the output:
+----+-------+ | Id | Name | +----+-------+ | 1 | NULL | | 2 | John | | 3 | NULL | | 4 | | | 5 | Carol | | 6 | | | 7 | NULL | +----+-------+ 7 rows in set (0.00 sec)
Here is the query to check field is empty or null or something else using case statement. The query is as follows:
mysql> select *,case -> when Name='' then 'It is an empty string' -> when Name is null then 'It is a NULL value' -> else concat(Name,' is a Name') -> END as ListOfValues -> from checkFieldDemo;
The following is the output:
+----+-------+-----------------------+ | Id | Name | ListOfValues | +----+-------+-----------------------+ | 1 | NULL | It is a NULL value | | 2 | John | John is a Name | | 3 | NULL | It is a NULL value | | 4 | | It is an empty string | | 5 | Carol | Carol is a Name | | 6 | | It is an empty string | | 7 | NULL | It is a NULL value | +----+-------+-----------------------+ 7 rows in set (0.00 sec)
Updated on: 30-Jul-2019
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