Update many flag columns given the value of other columns (NULL values) in the same record

Question

Given a table of input data I would like to have a set o "flag columns" that describe sibling columns of the same record.

• I am using Microsoft SQL Server 2005.
• First of all I need to load data in the target table, then I need to perform checks to put values in those flag columns.

Say for example I have a toy table like the following one:

CREATE TABLE zzz_test
             (
                          color        VARCHAR(10),
                          value_x      INTEGER    ,
                          value_y      INTEGER    ,
                          value_x_FLAG bit        ,
                          value_y_FLAG bit
             )

Then I have the following toy data (I need to repeat the INSERT/VALUES statements for every record because of the "old" 2005 SQL version):

INSERT zzz_test(color,value_x,value_y)
VALUES('red',1,NULL)
INSERT zzz_test(color,value_x,value_y)
VALUES('green',NULL,NULL)
INSERT zzz_test(color,value_x,value_y)
VALUES('red',NULL,2)
INSERT zzz_test(color,value_x,value_y)
VALUES('red',1,3)
INSERT zzz_test(color,value_x,value_y)
VALUES('black',NULL,1)
INSERT zzz_test(color,value_x,value_y)
VALUES(NULL,3,2)
INSERT zzz_test(color,value_x,value_y)
VALUES('black',1,2)
INSERT zzz_test(color,value_x,value_y)
VALUES('red',3,4)
INSERT zzz_test(color,value_x,value_y)
VALUES('green',1,1)
INSERT zzz_test(color,value_x,value_y)
VALUES('blue',5,NULL)

Now I would like to have a quick way to put values inside value_x_FLAG and value_y_FLAG evaluating if sibling columns value_x and value_y are NULL.

I know that there are functions like ISNULL(), or COALESCE(), but I do not think this is the case because I am trying to update a column given the value of another column.

I know I can use IF / ELSE statements but it's quite complicate to set all the cases of many boolean flags (2^n) to work all together in the same "update" statement of the flag variables.

How to deal with it?

After setting all the flags I would like to summarize in some way my table. For example I would like to have a COUNT on all the flag variables, then I would like to have a COUNT given the "color category".

Probably I do not need a set of support flag variables, but I would like to have them to make the table much more readable, and also the SQL code much more readable. Thanks!

Answer 1

try this, after all inserts, do

update zzz_test set value_x_FLAG = CASE value_x when null then 1 else 0 END, value_y_FLAG = CASE value_y when null then 1 else 0 END

hope it works!

edit: about the count, you can use group by clause everytime you need it, instead of have a flag saved in somewhere

select Color, Count(value_x_FLAG) from zzz_test  group by Color having value_x_FLAG != 0

this will return a 2 column table, with the color and int the other column the number of rows that have the flag = 1