Dynamic update statement with variable column names - sql

Question

We're looking to do an update in several SQL Server databases to change all NULL values in a certain table to be empty strings instead of NULL. We're potentially going to be doing this across hundreds of databases. The table name will always be the same, but the column names are variable based on how the front-end application is configured (don't judge... I didn't create this system).
Is there a way to do an update on all of these columns without knowing the column names ahead of time?

Answer 1

You can pass the name of the column in dynamic sql:
declare #sql nvarchar (1000);
set #sql = N'update table set ' + #column_name + '= ''''';
exec sp_executesql #sql;

Answer 2

You can look in the sys.columns table and join on the table name or object_id.
DECLARE #OBJ_ID INT
SELECT #OBJ_ID = OBJECT_ID
FROM SYS.tables
WHERE name = 'YOURTABLE'
SELECT * FROM SYS.columns
WHERE OBJECT_ID = #OBJ_ID
You could use the name field from the sys.columns query as a basis to perform the update on.

Answer 3

Assuming you want all columns of varchar/char types only (or change the type filter to whatever you need):
DECLARE #tableName varchar(10)
SET #tableName = 'yourtablenamehere'
DECLARE #sql VARCHAR(MAX)
SET #sql = ''
SELECT #sql = #sql + 'UPDATE ' + #tableName + ' SET ' + c.name + ' = '''' WHERE ' + c.name + ' IS NULL ;'
FROM sys.columns c
INNER JOIN sys.tables t ON c.object_id = t.object_id
INNER JOIN sys.types y ON c.system_type_id = y.system_type_id
WHERE t.name = #tableName AND y.name IN ('varchar', 'nvarchar', 'char', 'nchar')
EXEC (#sql)

Answer 4

This can be achieved with cursors. You first select the column names like #Darren mentioned, then you Set a Cursor with those values and loop:
Open oColumnsCursor
Fetch Next From oColumnscursor
Into #ColumnName
While ##FETCH_STATUS=0
Begin
Set #oQuery = 'Update [DB]..[Table] Set [' + #ColumnName + '] = ''NewValue'' Where [' + #ColumnName + '] = ''OldValue'''
Execute(#oQuery)
Fetch Next From oColumnscursor Into #ColumnName
Set #oCount = #oCount + 1
End
Close oColumnsCursor;
Deallocate oColumnsCursor;

Answer 5

This will work when you know the Table Name:
DECLARE #tableName varchar(10)
SET #tableName = 'Customers'
DECLARE #sql VARCHAR(MAX)
SET #sql = ''
SELECT #sql = #sql + 'UPDATE ' + #tableName + ' SET ' + c.name + ' = ISNULL('+ c.name +','''');'
FROM sys.columns c
INNER JOIN sys.tables t ON c.object_id = t.object_id
INNER JOIN sys.types y ON c.system_type_id = y.system_type_id
WHERE y.name IN ('varchar', 'nvarchar', 'char', 'nchar')
AND t.name = #tableName;
EXEC(#sql);
And this will iterate all Tables and all Columns in a Db:
DECLARE #sql VARCHAR(MAX)
SET #sql = ''
SELECT #sql = #sql + 'UPDATE ' + t.name + ' SET ' + c.name + ' = ISNULL('+ c.name +','''');'
FROM sys.columns c
INNER JOIN sys.tables t ON c.object_id = t.object_id
INNER JOIN sys.types y ON c.system_type_id = y.system_type_id
WHERE y.name IN ('varchar', 'nvarchar', 'char', 'nchar');
EXEC(#sql);

Answer 6

Below is the procedure.
ALTER PROCEDURE [dbo].[util_db_updateRow]
#colval_name NVARCHAR (30), -- column and values e.g. tax='5.50'
#idf_name NVARCHAR (300), -- column name
#idn_name NVARCHAR (300), -- column value
#tbl_name NVARCHAR (100) -- table name
AS
BEGIN
SET NOCOUNT ON;
DECLARE #sql NVARCHAR(MAX)
-- construct SQL
SET #sql = 'UPDATE ' + #tbl_name + ' SET ' + #colval_name +
' WHERE ' + #idf_name + '=' + #idn_name;
-- execute the SQL
EXEC sp_executesql #sql
SET NOCOUNT OFF
RETURN
END

Answer 7

Below is the stored procedure where you can pass Schema Name, Table Name and list of column names separted by comma.It works only in Sql Server 2016 or higher.
CREATE OR ALTER PROCEDURE UpdateData
(#SchemaName NVARCHAR(Max),#TableName NVARCHAR(MAX),#ColumnNames NVARCHAR(MAX))
AS
BEGIN
DECLARE #DynamicSql NVARCHAR(MAX);
SET #DynamicSql = 'UPDATE ' +'[' +#SchemaName+'].' + '[' +#TableName+']' +' SET ' + STUFF((SELECT ', [' + C.name + '] = ' + '''NEW_VALUE'''
FROM sys.columns C
INNER JOIN sys.tables T ON T.object_id = C.object_id
INNER JOIN sys.schemas S ON T.schema_id = S.schema_id
WHERE
T.name = #TableName
AND S.Name = #SchemaName
AND [C].[name] in (SELECT VALUE FROM string_split(#ColumnNames,','))
FOR XML PATH('')), 1,1, '')
print #DynamicSql;
EXEC (#DynamicSql);
END