How do you modify a table cell depending on its column type? - sql

Question

I want to update cells in an SQL table depending on the type of its column. More specifically, I want to replace NULL values by either '',0,0.0 or '1900-01-01' depending on the column type. The table has 60 columns and so a manual approach is awkward.
The approach I have tried uses metadata and I want to generate an update script.
Use case is for an import into Excel where the NULL values must be taken care off in a column type dependant way.

Answer 1

As discussed in the comments, the easiest way seems to be use ''. The only exception (I found) was for decimal/numeric, where implicit and explicit conversion is not allowed.
As shown below, you can write the statement out (but I exclude the decimal column) or do it dynamically:
USE Sandbox;
GO
CREATE TABLE TestTable (ID int IDENTITY(1,1),
SomeInt int,
SomeDecimal decimal(10,2),
SomeFloat float,
SomeMoney money,
SomeDate date,
SomeDatetime datetime,
SomeTime time,
SomeDatetime2 datetime2(1),
SomeVarbinary varbinary(12),
SomeVarchar varchar(10),
SomeBit bit);
INSERT INTO dbo.TestTable (SomeInt,
SomeDecimal,
SomeFloat,
SomeMoney,
SomeDate,
SomeDatetime,
SomeTime,
SomeDatetime2,
SomeVarbinary,
SomeVarchar,
SomeBit)
VALUES(NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL),
(NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL);
GO
UPDATE dbo.TestTable
SET SomeInt = ISNULL(SomeInt,''),
--SomeDecimal = ISNULL(SomeDecimal,''),
SomeFloat = ISNULL(SomeFloat,''),
SomeMoney = ISNULL(SomeMoney,''),
SomeDate = ISNULL(SomeDate,''),
SomeDatetime = ISNULL(SomeDatetime,''),
SomeTime = ISNULL(SomeTime,''),
SomeDatetime2 = ISNULL(SomeDatetime2,''),
SomeVarbinary = ISNULL(SomeVarbinary,CONVERT(varbinary,'')),
SomeVarchar = ISNULL(SomeVarchar,''),
SomeBit = ISNULL(SomeBit,'')
WHERE ID = 1;
GO
DECLARE #Schema sysname = N'dbo',
#Table sysname = N'TestTable';
DECLARE #SQL nvarchar(MAX);
SET #SQL = N'UPDATE ' + QUOTENAME(#Schema) + N'.' + QUOTENAME(#Table) + NCHAR(13) + NCHAR(10) +
N'SET ' + STUFF((SELECT N',' + NCHAR(13) + NCHAR(10) +
N' ' + QUOTENAME(C.COLUMN_NAME) + N' = ISNULL(' + QUOTENAME(C.COLUMN_NAME) + N',' + CASE C.DATA_TYPE WHEN N'decimal' THEN '0)'
WHEN N'numeric' THEN '0)'
ELSE N'CONVERT(' + QUOTENAME(C.DATA_TYPE) + N',N''''))'
END
FROM INFORMATION_SCHEMA.COLUMNS C
WHERE C.TABLE_SCHEMA = #Schema
AND C.TABLE_NAME = #Table
AND C.COLUMN_NAME != 'ID' --You'll need a better method to ignore your ID column
FOR XML PATH(N''),TYPE).value('.','nvarchar(MAX)'),1,7,N'') + NCHAR(13) + NCHAR(10) +
N'WHERE ID = 2;'; --you won't want this if you're doing every row.
PRINT #SQL;
EXEC sp_executesql #SQL;
GO
SELECT *
FROM dbo.TestTable;
GO
DROP TABLE dbo.TestTable
db<>fiddle
If you're using SQL Server 2017+, you can simplify the above by using STRING_AGG instead of FOR XML PATH and STUFF to create a "delimited" list of the columns in the table.

Answer 2

SELECT COLUMN_NAME AS colname, DATA_TYPE AS coltype
INTO #result_columns
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'mytable';
WITH cte(colname, default_value) AS (
SELECT colname,
CASE
WHEN coltype IN ('varchar','nvarchar') THEN ''''''
WHEN coltype IN ('int','money') THEN '0'
WHEN coltype IN ('date') THEN '''1900-01-01'''
WHEN coltype IN ('float') THEN '0.0'
END AS default_value
FROM #result_columns
)
SELECT 'UPDATE mytable SET ' + colname + '=' + default_value + ' WHERE ' + colname + ' IS NULL;'
FROM cte;
-- result :
UPDATE mytable SET Caracteristique='' WHERE Caracteristique IS NULL;
UPDATE mytable SET Couleur='' WHERE Couleur IS NULL;
UPDATE mytable SET Forme='' WHERE Forme IS NULL;
UPDATE mytable SET Machine='' WHERE Machine IS NULL;
UPDATE mytable SET QteChargee=0.0 WHERE QteChargee IS NULL;