I am going to continue my series of very short articles or tidbits on Transaction SQL string functions. I will exploring the LEFT() function today.
The LEFT() function takes the source string [S] and number of characters [X] as input and returns the [X] leftmost characters from string [S] as output.
The following example grabs the first word from a favorite movie title of mine.
|
1 2 |
-- Return first word select left('wizard of oz', 6) as str_word |
|
1 2 3 4 5 |
output: str_word ----------- wizard |
One thing to always worry about when using TSQL functions is how will it react with empty strings, NULL values, or invalid values? Both empty strings and NULL values as inputs return themselves as outputs. A negative number for input [X] will result in a error being throw.
|
1 2 3 4 5 6 7 8 |
-- Invalid length select left('wizard of oz', -1) as str_word -- Empty string returns empty string select left('', 6) as str_word -- Null returns Null select left(NULL, 6) as str_word |
|
1 2 3 4 5 6 7 8 9 10 11 |
output: Msg 536, Level 16, State 1, Line 2 Invalid length parameter passed to the left function. str_word -------- str_word -------- NULL |
Next time, I will be exploring the LEN() function.
