使用动态sql时,可能需要添加额外的子句,具体取决于满足某些条件。1 = 1子句在查询中没有任何意义(除了始终满足),它的唯一用途是降低用于生成查询的代码的复杂性。
例如,此伪代码
DECLARE
v_text VARCHAR2(2000) := 'SELECT * FROM table WHERE 1=1 ';
BEGIN
IF condition_a = met THEN
v_text := v_text ||' AND column_1 = ''A'' ';
END IF;
IF condition_b = also_met THEN
v_text := v_text ||' AND column_2 = ''B'' ';
END IF;
execute_immediate(v_text);
END;
比下面的伪代码更简单,并且随着添加更多子句,它只会变得更加混乱。
DECLARE
v_text VARCHAR2(2000) := 'SELECT * FROM table ';
BEGIN
IF condition_a = met THEN
v_text := v_text ||' WHERE column_1 = ''A'' ';
END IF;
IF condition_b = also_met AND
condition_a != met THEN
v_text := v_text ||' WHERE column_2 = ''B'' ';
ELSIF condition_b = also_met AND
condition_a = met THEN
v_text := v_text ||' AND column_2 = ''B'' ';
END IF;
execute_immediate(v_text);
END;