Executing Dynamic Query Statements

You can perform dynamic queries openGauss 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 data set, use OPEN FOR.

EXECUTE IMMEDIATE

Figure 1 shows the syntax diagram.

Figure 1 EXECUTE IMMEDIATE dynamic_select_clause::=

Figure 2 shows the syntax diagram for using_clause.

Figure 2 using_clause::=

The above syntax diagram is explained as follows:

  • define_variable: specifies variables to store single-line query results.

  • USING IN bind_argument: specifies where the variable passed to the dynamic SQL value is stored, that is, in the dynamic placeholder of dynamic_select_string.

  • USING OUT bind_argument: specifies where the dynamic SQL returns the value of the variable.

    NOTICE:

    • 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.

OPEN FOR

Dynamic query statements can be executed by using OPEN FOR to open dynamic cursors.

Figure 3 shows the syntax diagram.

Figure 3 open_for::=

Parameter description:

  • cursor_name: specifies the name of the cursor to be opened.
  • dynamic_string: specifies the dynamic query statement.
  • **USING **value: applies when a placeholder exists in dynamic_string.

For use of cursors, see Cursors.

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