Variable value was lost when while loop finished - sql

Question

I want to set some default values to some table by using dynamic SQL in SQL Server, so I write 2 while loop, one is for tables and one is for columns in that table. so the outer loop is used to iterate table and the inner loop is used to iterate columns according to different data types the default will vary from one to other. So I need to catenate strings to build the dynamic SQL, please see my code below:
DECLARE #V_TABLE_LIST TABLE (TABLE_NAME VARCHAR(300))
DECLARE #V_COLUMN_LIST TABLE (TABLE_NAME VARCHAR(300), COLUMN_NAME VARCHAR(300), DATA_TYPE VARCHAR(300))
DECLARE #V_TABLE_NAME VARCHAR(300)
DECLARE #V_TABLE_NAME2 VARCHAR(300)
DECLARE #V_COLUMN_NAME VARCHAR(300)
DECLARE #V_DATA_TYPE VARCHAR(300)
DECLARE #V_SQL_ENABLE_IDENTITY_INSERT VARCHAR(200)
DECLARE #V_SQL_INSERT VARCHAR(3500)
DECLARE #V_SQL_COLUMN_LIST_NAME VARCHAR(3000)
DECLARE #V_SQL_COLUMN_LIST_VALUE VARCHAR(3000)
DECLARE #V_SQL_DISABLE_IDENTITY_INSERT VARCHAR(200)
INSERT INTO #V_TABLE_LIST
(TABLE_NAME)
SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_NAME LIKE 'DIM%' AND TABLE_TYPE = 'BASE TABLE'
AND TABLE_NAME NOT IN ('DIM_DATE') AND TABLE_NAME = 'DIM_ASSET'
--loop through each table
WHILE (SELECT COUNT(*) FROM #V_TABLE_LIST) > 0
BEGIN
SELECT TOP 1
#V_TABLE_NAME = TABLE_NAME
FROM #V_TABLE_LIST
--PRINT(#V_TABLE_NAME)-------------
SET #V_SQL_ENABLE_IDENTITY_INSERT = 'SET IDENTITY_INSERT ' + #V_TABLE_NAME + ' ON'
SET #V_SQL_DISABLE_IDENTITY_INSERT = 'SET IDENTITY_INSERT ' + #V_TABLE_NAME + ' OFF'
--load column info into #v_column_list table variable for each table
INSERT INTO #V_COLUMN_LIST
(TABLE_NAME, COLUMN_NAME, DATA_TYPE)
SELECT TABLE_NAME, COLUMN_NAME, DATA_TYPE
FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = #V_TABLE_NAME
SET #V_SQL_INSERT = ''
SET #V_SQL_COLUMN_LIST_NAME = ''
SET #V_SQL_COLUMN_LIST_VALUE = ''
--loop through each column for each table
WHILE (SELECT COUNT(*) FROM #V_COLUMN_LIST) > 0
BEGIN
SELECT TOP 1
#V_TABLE_NAME2 = TABLE_NAME
,#V_COLUMN_NAME = COLUMN_NAME
,#V_DATA_TYPE = DATA_TYPE
FROM #V_COLUMN_LIST
SET #V_SQL_COLUMN_LIST_NAME = #V_SQL_COLUMN_LIST_NAME + #V_COLUMN_NAME + ' --' + #V_DATA_TYPE +CHAR(10) + ','
SET #V_SQL_COLUMN_LIST_VALUE = #V_SQL_COLUMN_LIST_VALUE +
CASE WHEN #V_DATA_TYPE IN ('VARCHAR','NVARCHAR','CHAR', 'NCHAR') THEN '''UNKNOWN'''
WHEN #V_DATA_TYPE IN ('bigint', 'INT', 'smallint', 'DECIMAL','NUMERIC','MONEY','SMALLMONEY') THEN '-1'
WHEN #V_DATA_TYPE IN ('BIT', 'TINYINT') THEN NULL
WHEN #V_DATA_TYPE IN ('DATE', 'DATETIME','SMALLDATETIME','DATETIMEOFFSET','DATETIME2') THEN '''1957-01-01'''
ELSE ''
END + ' --' + #V_COLUMN_NAME + CHAR(10) + ','
DELETE FROM #V_COLUMN_LIST WHERE TABLE_NAME = #V_TABLE_NAME2 AND COLUMN_NAME = #V_COLUMN_NAME
--PRINT(#V_SQL_COLUMN_LIST_VALUE)
END
PRINT(#V_SQL_COLUMN_LIST_NAME)
PRINT(#V_SQL_COLUMN_LIST_VALUE)
--PRINT(#V_SQL_ENABLE_IDENTITY_INSERT)
SET #V_SQL_INSERT = 'INSERT INTO ' + #V_TABLE_NAME + CHAR(10)
+ '('
+ #V_SQL_COLUMN_LIST_NAME
+ ')'
+ ' VALUES ' + CHAR(10)
+ '(' + CHAR(10)
+ #V_SQL_COLUMN_LIST_VALUE
+ ')'
--PRINT(#V_SQL_INSERT)
--PRINT(#V_SQL_DISABLE_IDENTITY_INSERT)
DELETE FROM #V_COLUMN_LIST
DELETE FROM #V_TABLE_LIST WHERE TABLE_NAME = #V_TABLE_NAME
END
I added 2 print statements:
PRINT(#V_SQL_COLUMN_LIST_NAME) ---the concatenated field list can be printed out normally
PRINT(#V_SQL_COLUMN_LIST_VALUE) ---cannot print concatenated default value list , why?
as you can see the two print statements are the next step for the finishing of inner loop, but the first print statement can print out the something and the second one is empty, I checked the code a long time, I cannot find why the second print statement output empty string. Any logic errors in the code above?

Answer 1

This row sets the entire result to NULL if any column of BIT or TINYINT type is met.
WHEN #V_DATA_TYPE IN ('BIT', 'TINYINT') THEN NULL
Should be
WHEN #V_DATA_TYPE IN ('BIT', 'TINYINT') THEN 'NULL'
the same way as any other constant in a dynamic sql.