如果其中之一为空，则联接列

Question

I have 3 columns:

col1, int 
col2, char(10) 
col3, char(11)

only one of them has any value in them, and it can be either one of them.

i want to check which columns are null and add the one, whcih has a value to a fourth column: col4.

i use T-SQL

Answer 1

Try this

select col1,col2,col3, coalesce(col1, coalesce(col2,col3)) as col4
from your_table

COALESCE returns the first non-null expr in the expression list. If all occurrences of expr evaluate to null, then the function returns null.

Answer 2

You could use IS NULL comparison to return a boolean true or false for each column and COALESCE() to find the first non-null value among all the columns

SELECT
  col1 IS NULL AS col1_null,
  col2 IS NULL AS col2_null,
  col3 IS NULL AS col3_null,
  COALESCE(cast(col1 as char(11)), cast(col2 as char(11)), cast(col3 as char(11)) AS first_not_null_val
FROM table

Order of columns provided within COALESCE() function matters, but since you have only one of those three that is not null, then it would always return that one.

Note : You need to cast your columns to the same datatype for COALESCE() . Since your upper bound is char(11) because it covers both char(10) and int type I've come up with that. I imagine that you want to keep the spaces which is why you use char in the first place.

Answer 3

SELECT COALESCE(CONVERT(CHAR(11), col1), CONVERT(CHAR(11), col2), col3)
FROM yourtable;

TSQL: COALESCE