如何在sql查询（PostgreSQL）中管理空字符串或日期

PostgreSQL 11.1 对于下面的sql查询，其中$1和$2是字符串，$3是时间戳，如何重写下面的查询，以便$3中的空值允许选择每个日期（不仅仅是空日期）

也就是说，如果$3为空，则应减少为：

SELECT lastname, firstname, birthdate FROM patients 
               WHERE UPPER(lastname) LIKE UPPER($1)||'%' and UPPER(firstname) LIKE UPPER($2)||'%' 
            UNION
            SELECT lastname, firstname, birthdate FROM appointment_book 
               WHERE UPPER(lastname) LIKE UPPER($1)||'%' and UPPER(firstname) LIKE UPPER($2)||'$' 

---

未经测试，但我认为您可以使用

CASE

表达式处理此问题

SELECT lastname, firstname, birthdate FROM patients p
  WHERE UPPER(p.lastname) LIKE UPPER($1)||'%'
  AND   UPPER(p.firstname) LIKE UPPER($2)||'%'
  AND   (CASE WHEN $3 IS NULL THEN TRUE
         ELSE                      p.birthdate::date = $3::date
         END)
UNION
SELECT lastname, firstname, birthdate FROM appointment_book ab
  WHERE UPPER(ab.lastname) LIKE UPPER($1)||'%'
  AND   UPPER(ab.firstname) LIKE UPPER($2)||'%'
  AND   (CASE WHEN $3 IS NULL THEN TRUE
         ELSE                      ab.birthdate::date = $3::date
         END);

SELECT lastname, firstname, birthdate FROM patients p
  WHERE UPPER(p.lastname) LIKE UPPER($1)||'%'
  AND   UPPER(p.firstname) LIKE UPPER($2)||'%'
  AND   (CASE WHEN $3 IS NULL THEN TRUE
         ELSE                      p.birthdate::date = $3::date
         END)
UNION
SELECT lastname, firstname, birthdate FROM appointment_book ab
  WHERE UPPER(ab.lastname) LIKE UPPER($1)||'%'
  AND   UPPER(ab.firstname) LIKE UPPER($2)||'%'
  AND   (CASE WHEN $3 IS NULL THEN TRUE
         ELSE                      ab.birthdate::date = $3::date
         END);