Constant INTROSPECT_COLUMNS_SQL 

pub const INTROSPECT_COLUMNS_SQL: &str = "\
    SELECT column_name, data_type, is_nullable, \
           (SELECT COUNT(*) FROM information_schema.table_constraints tc \
            JOIN information_schema.key_column_usage kcu \
              ON tc.constraint_name = kcu.constraint_name \
            WHERE tc.table_name = c.table_name \
              AND kcu.column_name = c.column_name \
              AND tc.constraint_type = 'PRIMARY KEY') as is_pk \
    FROM information_schema.columns c \
    WHERE table_schema = 'public' AND table_name = $1 \
    ORDER BY ordinal_position";

SQL to list columns for a given table. Use with parameter: table_name.