c# - MySQL 中具有多个 SELECT 的 IF 语句

Question

我正在使用 MySQL 和 Visual Studio 2010 C# 语言。

我需要查询。

SELECT a field, if this field is null or equals to 0

再做一个SELECT如果不同<>来自 null或 0 .再做一个SELECT .

我也尝试按照您在上面写标题时出现的建议进行操作，但没有任何效果。

类似的东西:

SELECT cart.cod_dependent (if cart.cod_dependent <> 0, Select ass.matricula, ass.nome, ass.situacao_social, ass.categoria, ELSE IF cart.cod_dependent = null Make another select)

每个选择将在不同的表中，但都在同一个数据库中。

------ 更新 10/08/2012 09:59 --------现在我正在尝试你所说的Radu Bompa，但它说“执行命令期间遇到 fatal error ”=\。

 MySqlCommand cmd = new MySqlCommand();
  string sql = @"SELECT @cod_dep = cart.cod_dependente FROM carteiras as cart
  IF @cod_dep IS NULL
  BEGIN
  SELECT ass.matricula, ass.nome, ass.situacao_social, ass.categoria FROM associados AS ass INNER JOIN categorias AS cat ON cat.codigo = ass.categoria,
  INNER JOIN situacoes_social AS ss ON ass.situacao_social = ss.codigo
  END
  ELSE
  BEGIN
  SELECT dep.nome, dep.matricula, dep.situacao_social, ss.descricao FROM dependentes INNER JOIN situacao_social as ss dep.situacao_social = ss.codigo
  END
  WHERE cart.numero = @carteira";
  cmd.CommandText = sql;
  cmd.CommandType = CommandType.Text;
  string dependente = "";
  cmd.Parameters.Add(new MySqlParameter("@carteira", MySqlDbType.Int32)).Value = carteira;
  DataSet ds = _dal.Consultar(cmd);

Answer 1

也许这样的事情可行:

SELECT @SomeValue = cart.cod_dependent FROM cart   
--@SomeValue is a variable, declared for this purpose
IF @SomeValue IS NULL
BEGIN
  SELECT ass.matricula, ass.nome, ass.situacao_social, ass.categoria FROM table2
END
ELSE
BEGIN
  SELECT field FROM table3
END

您也可以尝试使用 stored procedure .