Why do we use execute immediate in plsql? - plsql

Question

Why do we use "Execute immediate" in plsql? I know we use it to execute dynamic sql statements. But still I'm unable to convince interviewer. Could anybody give me an exact and proper answer for this? Though I use it everyday, but still unable to explain it. One thing I know is, it's used in DML statements and to retrieve multiple rows through select statement. Please give an exact definition for using "Execute immediate".

Answer 1

EXECUTE IMMEDIATE enables execution of a DML or DDL statement which is held as a string and only evaluated at runtime. This enables one to dynamically create the statement based on program logic. EXECUTE IMMEDIATE is also the only way you can execute DDL within a PL/SQL block. See the Oracle Manual for a complete and thorough review of these features.
While this is a very useful facility it should be used with care. Unless there is an explicit need for dynamic sql then it is better to directly declare the sql within your PL/SQL code. This will enable Oracle to parse the SQL at compile time for validity and also reduce overhead when executing the pre-compiled statement. Also you need to be very careful to avoid SQL injection attacks when dynamically building SQL.

Answer 2

For example, let's say you have some kind of application where users define their company and all the work they do. If you want to make it dynamically for users, then you can give them option to create their own models(tables). Since you do not know how many tables they will have, and how many attributes this tables will have you can use execute immediate.

Answer 3

DDL Statement in Procedures or Anonymous PLSQL blocks
Here is an example showing how to use dynamic DDL to create, drop and re-create a table:
BEGIN
EXECUTE IMMEDIATE 'create table abcd (efgh NUMBER)';
EXECUTE IMMEDIATE 'drop table abcd';
EXECUTE IMMEDIATE 'create table abcd (efgh VARCHAR2(10))';
END;
You can use this method to execute any DDL.
Though it's not suggested to use Execute Immediate for DDL, rather Global Temp Table should be used.
To execute DML statements in Procedures or Anonymous PLSQL blocks
To execute DML commands more often than DDL. With dynamic SQL you can issue inserts, updates and deletes just as you can with static SQL:
BEGIN
EXECUTE IMMEDIATE 'INSERT INTO abcd (efgh) VALUES (:text_string)'
USING 'ijkl';
EXECUTE IMMEDIATE 'INSERT INTO abcd (efgh) VALUES (:text_string)'
USING 'mnop';
EXECUTE IMMEDIATE 'UPDATE abcd ' ||
'SET efgh = :text_string WHERE efgh = :second_string'
USING 'qrst', 'mnop';
EXECUTE IMMEDIATE 'DELETE FROM abcd ' ||
'WHERE efgh = :text_string '
USING 'qrst';
END;
In Select queries with bind variables
As useful as DDL and DML are, a database is not very useful if you can't get your data out. You can also use execute immediate to select your data back out.
DECLARE
v_data abcd.efgh%TYPE;
v_data_row abcd%ROWTYPE;
BEGIN
EXECUTE IMMEDIATE 'SELECT efgh FROM abcd WHERE efgh = :text_string'
INTO v_data
USING 'ijkl';
DBMS_OUTPUT.PUT_LINE( 'Column Variable: ' || v_data );
EXECUTE IMMEDIATE 'SELECT * FROM abcd WHERE efgh = :text_string'
INTO v_data_row
USING 'ijkl';
DBMS_OUTPUT.PUT_LINE( 'Row Variable: ' || v_data_row.efgh );
END;
INFO: Column Variable: ijkl
INFO: Row Variable: ijkl