How to Change datatype of all column to Unicode datatype for all base table in a database

Question

Due to storing values from language specific diacritics (Spanish, French, German) I am trying to change the datatype of a column to Unicode datatype.

• Varchar to nvarchar
• char to nchar

So all column datatype to its respective Unicode datatype.

For all tables in a specific database.

Can it be possible to do in a single statement? Because doing with alter statement is time consuming.

ALTER TABLE dbo.Employee 
ALTER COLUMN FirstName NVARCHAR(255) NOT NULL

Many thanks.

Answer 1

First we create a temporary table and define the variables we need for the changes.

Then we fill the table by fetching the columns that need to change. I entered the fetch command below and everything is clear.

Then, for each row in the table, we make the desired changes in the database.

Also, a column in a table may have a value of NULL , so you must replace the NULL values with a value before changing the column. I replaced the NULL values with a value of 0 .

The code below works perfectly and correctly.

Only I entered dbo for schema name in search of columns. See what your database schema name is

--Container to Insert Id which are to be iterated
Declare @temp1 Table
(
  tablename varchar(100),
  columnname varchar(100),
  columnlength varchar(100),
  columntype varchar(100)
)
--Container to Insert records in the inner select for final output

Insert into @temp1 

SELECT t.TABLE_NAME,c.COLUMN_NAME,c.CHARACTER_MAXIMUM_LENGTH,c.DATA_TYPE FROM information_schema.tables t
join INFORMATION_SCHEMA.COLUMNS c on t.TABLE_NAME = c.TABLE_NAME
WHERE t.table_schema='dbo'
and (DATA_TYPE = 'varchar' OR DATA_TYPE = 'char')

-- Keep track of @temp1 record processing
Declare @tablename varchar(100)
Declare @columnname varchar(100)
Declare @columnlength varchar(100)
Declare @columntype varchar(100)
Declare @SQL VarChar(1000)
Declare @vary varchar(100)
Declare @final varchar(1000)

While((Select Count(*) From @temp1)>0)
Begin


  Set @tablename=(Select Top 1 tablename From @temp1)
  Set @columnname=(Select Top 1 columnname From @temp1)
  Set @columnlength=(Select Top 1 columnlength From @temp1)
  Set @columntype=(Select Top 1 columntype From @temp1)


  if(@columntype = 'varchar')
    Set @columntype='nvarchar'
  else
    Set @columntype='nchar'
  --set null value with 0 value

  SELECT @SQL = 'UPDATE ' + @tablename + ' SET ' + @columnname + ' = 0 WHERE ' + @columnname  + ' IS NULL'
  Exec ( @SQL)


  SELECT @SQL = 'ALTER TABLE '
  SELECT @SQL = @SQL + @tablename
  select @vary = ' ALTER COLUMN ' + @columnname + ' ' + @columntype + '(' + @columnlength + ') NOT NULL'
  select @final = @sql + @vary

  --select @final
  Exec ( @final)

  Delete @temp1 Where tablename=@tablename and columnname = @columnname
End