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What does <=> in MySQL mean and do?
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It (<>) is a function that is used to compare values in database table. != (Not equal to) functions the same as the <> (Not equal to) comparison operator. Follow this answer to receive notifications.
In relational database management systems, a query is any command used to retrieve data from a table. In Structured Query Language (SQL), queries are almost always made using the SELECT statement.
<> this symbol means not equal in sql. Basically <> this symbol used in sql when we write Non-Equi join query.
Difference between SQL Not Equal Operator <> and != to do inequality test between two expressions. Both operators give the same output. The only difference is that '<>' is in line with the ISO standard while '!= ' does not follow ISO standard.
The manual says it all:
NULL-safe equal. This operator performs an equality comparison like the = operator, but returns 1 rather than NULL if both operands are NULL, and 0 rather than NULL if one operand is NULL.
mysql> select NULL <=> NULL;
+---------------+
| NULL <=> NULL |
+---------------+
| 1 |
+---------------+
1 row in set (0.00 sec)
mysql> select NULL = NULL;
+-------------+
| NULL = NULL |
+-------------+
| NULL |
+-------------+
1 row in set (0.00 sec)
mysql> select NULL <=> 1;
+------------+
| NULL <=> 1 |
+------------+
| 0 |
+------------+
1 row in set (0.00 sec)
mysql> select NULL = 1;
+----------+
| NULL = 1 |
+----------+
| NULL |
+----------+
1 row in set (0.00 sec)
mysql>
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