Transformar datas em sql

select * from prre where convert(varchar(8),dtref,112)>='20130930'

Update query com troca de caractéres na string

update tabela

set campo1 = replace(campo1, RIGHT(campo1,1),'B')

where right(campo1,1)='A' and SOC_0='SOCxx' and DAT_0>='2019/01/01' and DAT_0<='2019/06/18';

SQL DELETE

Exemplo

DELETE FROM Customers
WHERE CustomerName='Alfreds Futterkiste' AND ContactName='Maria Anders';

Varchar invalid for Sum operator

Exemplo de erro:
Msg 8117, Level 16, State 1, Line 1
Operand data type varchar is invalid for sum operator.

Exemplo de solução:
Select Sum(isnull(cast(AMT as float),0)) as Amt
from dbo.Cos

Backup de tabela de base de dados para a mesma instância

select * into [base de dados destino].[schema].[Tabela_backup] from [base de dados origem].[schema].[Tabela]