How to get first character of a string in SQL?

问题:

I have a SQL column with a length of 6. Now want to take only the first char of that column. Is there any string function in SQL to do this?

回答1:

LEFT(colName, 1) will also do this, also. It's equivalent to SUBSTRING(colName, 1, 1).

I like LEFT, since I find it a bit cleaner, but really, there's no difference either way.

回答2:

I prefer:

SUBSTRING (my_column, 1, 1)

because it is Standard SQL-92 syntax and therefore more portable.

---

Strictly speaking, the standard version would be

SUBSTRING (my_column FROM 1 FOR 1)

The point is, transforming from one to the other, hence to any similar vendor variation, is trivial.

p.s. It was only recently pointed out to me that functions in standard SQL are deliberately contrary, by having parameters lists that are not the conventional commalists, in order to make them easily identifiable as being from the standard!

回答3:

SUBSTRING ( MyColumn, 1 , 1 ) for the first character and SUBSTRING ( MyColumn, 1 , 2 ) for the first two.

回答4:

It is simple to achieve this by following:

DECLARE @SomeString NVARCHAR(20) = 'This is some string'
DECLARE @Result NVARCHAR(20)

and either

SET @Result = SUBSTRING(@SomeString, 2, 3)
SELECT @Result

@Result: his

-OR-

SET @Result = LEFT(@SomeString, 6)
SELECT @Result

@Result: This i

回答5:

SELECT SUBSTR(thatColumn, 1, 1) As NewColumn from student

回答6:

INPUT

STRMIDDLENAME
--------------
Aravind Chaterjee
Shivakumar
Robin Van Parsee

SELECT STRMIDDLENAME, 
CASE WHEN INSTR(STRMIDDLENAME,' ',1,2) != 0 THEN SUBSTR(STRMIDDLENAME,1,1) || SUBSTR(STRMIDDLENAME,INSTR(STRMIDDLENAME,' ',1,1)+1,1)||
SUBSTR(STRMIDDLENAME,INSTR(STRMIDDLENAME,' ',1,2)+1,1)
WHEN INSTR(STRMIDDLENAME,' ',1,1) != 0 THEN SUBSTR(STRMIDDLENAME,1,1) || SUBSTR(STRMIDDLENAME,INSTR(STRMIDDLENAME,' ',1,1)+1,1)
ELSE SUBSTR(STRMIDDLENAME,1,1)
END AS FIRSTLETTERS
FROM Dual;

OUTPUT
STRMIDDLENAME                    FIRSTLETTERS
---------                        -----------------
Aravind Chaterjee                AC           
Shivakumar                       S
Robin Van Parsee                 RVP

回答7:

If you search the first char of string in Sql string

SELECT CHARINDEX('char', 'my char')

=> return 4