# String Functions
+ Perform an operation on a string, for example:
  + Calculating string length
  + Extracting a substring
  + Searching or replacing a substring
  + Case conversion
+ A string function can return a numeric value or a string
+ For example:
```
tidb> SELECT LENGTH(REPEAT('X',100000));
+----------------------------+
| LENGTH(REPEAT('X',100000)) |
+----------------------------+
|                     100000 |
+----------------------------+
1 row in set (0.00 sec)

```

------------------------------------------------------------
Note: REPEAT () can be used to generate large string and may be useful during the course. 

```
tidb> select REPEAT('xc',10);
+----------------------+
| REPEAT('xc',10)      |
+----------------------+
| xcxcxcxcxcxcxcxcxcxc |
+----------------------+
1 row in set (0.00 sec)
```

TiDB supports the use of most string function provided in MySQL 5.7.