在单引号中设置参数值的Postgres准备语句错误

Question

I am using parameterized query to the Postgres database in C#.

NpgsqlCommand command = new NpgsqlCommand("(SELECT * " +
    "FROM ABC AS abc " +
    " WHERE abc.SomeDate >= date_trunc('month', current_date) + interval '@periods' ");

command.Parameters.AddWithValue("periods", NpgsqlDbType.Text, periods);

where periods value format = '-5 years' or '-2 years'

On executing error is

22007: invalid input syntax for type interval: "@periods"

When I remove ' (single quote) from the @periods , It gives the error:

Error: 42601: syntax error at or near "$2"

Please suggest a way. Thanks.

Answer 1

You can't use parameter placeholders inside literals this way. Instead of writing interval '@param' , just write @param : Npgsql transmits the type information to PostgreSQL in the protocol with the parameter. In some cases you may need to specify NpgsqlDbType on your parameter to tell Npgsql which type to send (but in most cases it is inferred correctly from the CLR type).