The simplest way to execute an arbitrary SQL statement is to use the command EXECUTE IMMEDIATE. For example:

EXEC SQL BEGIN DECLARE SECTION;
const char *stmt = "CREATE TABLE test1 (...);";
EXEC SQL END DECLARE SECTION;

EXEC SQL EXECUTE IMMEDIATE :stmt;

EXECUTE IMMEDIATE can be used for SQL statements that do not return a result set (e.g., DDL, INSERT, UPDATE, DELETE). You cannot execute statements that retrieve data (e.g., SELECT) this way. The next section describes how to do that.

A more powerful way to execute arbitrary SQL statements is to prepare them once and execute the prepared statement as often as you like. It is also possible to prepare a generalized version of a statement and then execute specific versions of it by substituting parameters. When preparing the statement, write question marks where you want to substitute parameters later. For example:

EXEC SQL BEGIN DECLARE SECTION;
const char *stmt = "INSERT INTO test1 VALUES(?, ?);";
EXEC SQL END DECLARE SECTION;

EXEC SQL PREPARE mystmt FROM :stmt;
 ...
EXEC SQL EXECUTE mystmt USING 42, 'foobar';

When you don't need the prepared statement anymore, you should deallocate it:

EXEC SQL DEALLOCATE PREPARE name;

To execute an SQL statement with a single result row, EXECUTE can be used. To save the result, add an INTO clause.

EXEC SQL BEGIN DECLARE SECTION;
const char *stmt = "SELECT a, b, c FROM test1 WHERE a > ?";
int v1, v2;
VARCHAR v3[50];
EXEC SQL END DECLARE SECTION;

EXEC SQL PREPARE mystmt FROM :stmt;
 ...
EXEC SQL EXECUTE mystmt INTO :v1, :v2, :v3 USING 37;

An EXECUTE command can have an INTO clause, a USING clause, both, or neither.

If a query is expected to return more than one result row, a cursor should be used, as in the following example. (See Section 34.3.2 for more details about the cursor.)

EXEC SQL BEGIN DECLARE SECTION;
char dbaname[128];
char datname[128];
char *stmt = "SELECT u.usename as dbaname, d.datname "
             "  FROM pg_database d, pg_user u "
             "  WHERE d.datdba = u.usesysid";
EXEC SQL END DECLARE SECTION;

EXEC SQL CONNECT TO testdb AS con1 USER testuser;
EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT;

EXEC SQL PREPARE stmt1 FROM :stmt;

EXEC SQL DECLARE cursor1 CURSOR FOR stmt1;
EXEC SQL OPEN cursor1;

EXEC SQL WHENEVER NOT FOUND DO BREAK;

while (1)
{
    EXEC SQL FETCH cursor1 INTO :dbaname,:datname;
    printf("dbaname=%s, datname=%s\n", dbaname, datname);
}

EXEC SQL CLOSE cursor1;

EXEC SQL COMMIT;
EXEC SQL DISCONNECT ALL;

The do statement must be in language pl/sql.

EXEC SQL BEGIN DECLARE SECTION;
int id = 1;
int iReturnCode = -1;
EXEC SQL END DECLARE SECTION;


EXEC SQL create table t1(
    id integer,
    val text);

EXEC SQL insert into t1 values
    (1, 'a'),
    (2, null),
    (4, 'd');

EXEC SQL 
Do $$ 
begin
    begin
    update t1 set val = 'C' where id = :id;

    :iReturnCode = 0;
    :id = :id + 1;

    if SQL%NOTFOUND then
        :iReturnCode = 123;
    end if;
    
    exception
        when others then
            :iReturnCode = 456;
    end;
end;
$$ Language plorasql;

Every variable with ':' is recognized as a parameter, and the parameter's mode is inout.