Executing Dynamic Query Statements

You can perform dynamic queries GaussDB provides two modes: EXECUTE IMMEDIATE and OPEN FOR. EXECUTE IMMEDIATE dynamically executes SELECT statements and OPEN FOR combines use of cursors. If you need to store query results in a dataset, use OPEN FOR.

EXECUTE IMMEDIATE

Figure 1 shows the syntax diagram.

Figure 1 EXECUTE IMMEDIATE dynamic_select_clause::=
Click to enlarge

Figure 2 shows the syntax diagram for using_clause.

Figure 2 using_clause::=
Click to enlarge

The above syntax diagram is explained as follows:

define_variable: specifies a variable to store single-row query results.
USING IN bind_argument: specifies the variable whose value is passed to the dynamic SQL statement. The variable is used when a dynamic placeholder exists in dynamic_select_string.
USING OUT bind_argument: specifies the variable that stores a value returned by the dynamic SQL statement.
- In query statements, INTO and OUT cannot coexist.
- A placeholder name starts with a colon (:) followed by digits, characters, or strings, corresponding to bind_argument in the USING clause.
- bind_argument can only be a value, variable, or expression. It cannot be a database object such as a table name, column name, and data type. That is, bind_argument cannot be used to transfer schema objects for dynamic SQL statements. If a stored procedure needs to transfer database objects through bind_argument to construct dynamic SQL statements (generally, DDL statements), you are advised to use double vertical bars (||) to concatenate dynamic_select_clause with a database object.
- A dynamic PL/SQL block allows duplicate placeholders. That is, a placeholder can correspond to only one bind_argument in the USING clause. When the GUC parameter behavior_compat_options is set to dynamic_sql_compat, the bind arguments in the USING clause are matched in sequence based on the placeholder sequence. Duplicate placeholders will not be identified as the same placeholder.