我一直在努力弄清楚如何使用PostgreSQL在WHERE子句中放置CASE表达式。我需要将字符串转换为日期（如第3行所示）。这工作得很好。当我试图在WHERE子句中提取CURRENT_DATE时，我遇到了错误。这是最好的方法吗？任何建议都是非常欢迎的。

SELECT 
CASE WHEN
multi_app_documentation.nsma1_code = 'DATE' THEN TO_DATE(multi_app_documentation.nsma1_ans, 'MMDDYYYY') END AS "Procedure Date",
    ' ' AS "Case Confirmation Number",
    ip_visit_1.ipv1_firstname AS "Patient First", 
    ip_visit_1.ipv1_lastname AS "Patient Last", 
    visit.visit_sex AS "Patient Gender", 
    TO_CHAR(visit.visit_date_of_birth, 'MM/DD/YYYY') AS "DOB", 
    visit.visit_id AS "Account Number", 
    visit.visit_mr_num AS "MRN",
    ' ' AS "Module",
    ' ' AS "Signed off DT", 
    CASE WHEN
    multi_app_documentation.nsma1_code = 'CRNA' THEN multi_app_documentation.nsma1_ans END AS "Primary CRNA",
    ' ' AS "Secondary CRNA",
    ' ' AS "Primary Anesthesiologist",
' ' AS "Secondary Anesthesiologist",
' ' AS "Canceled Yes/No" 
FROM
    multi_app_documentation
    INNER JOIN ip_visit_1 ON multi_app_documentation.nsma1_patnum = ip_visit_1.ipv1_num
    INNER JOIN visit ON ip_visit_1.ipv1_num = visit.visit_id 
WHERE
CASE
        
        WHEN ( multi_app_documentation.nsma1_code = 'DATE' AND TO_DATE( multi_app_documentation.nsma1_ans, 'MMDDYYYY' ) = CURRENT_DATE END ) 
        AND multi_app_documentation.nsma1_ans IS NOT NULL 
ORDER BY
    ip_visit_1.ipv1_lastname ASC