How to use SQL Conditional statements in SQL

Question

I'm working on a BIRT Reporting. What I need to do is, If the Column1 value is Approved, Copy Column 2 value to Column 3 else null

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SELECT pr.prnum,prline.prlinenum,prline.itemnum,prline.description,prline.orderqty,prline.ponum,pr.status as "PRSTATUS",
postatusappr.changedate as "POAPPRDATE", matrectrans.actualdate as "ACTUALDELIVDATE", prstatuswappr.changedate as "PRCREATED",
prstatusappr.changedate as "PRAPPRDATE", days (current date) - days(date(prstatusappr.changedate)) as "NOOFDAYSAFTERPRAPPR",
INTEGER(days (current date) - days(date(prstatusappr.changedate)))/7 as "NOOFWEEKSAFTERPRAPPR",
INTEGER(days (current date) - days(date(postatusappr.changedate)))/7 as "NOOFWEEKSAFTERPOAPPR" FROM pr pr
LEFT JOIN prline prline ON prline.prnum = pr.prnum AND prline.siteid = pr.siteid
LEFT JOIN poline poline ON poline.ponum = prline.ponum AND poline.siteid = pr.siteid
LEFT JOIN postatus postatusappr ON postatusappr.ponum = poline.ponum AND postatusappr.siteid = pr.siteid AND postatusappr.status = 'APPR'
LEFT JOIN matrectrans matrectrans ON matrectrans.ponum = poline.ponum AND matrectrans.polinenum = poline.polinenum AND matrectrans.positeid = pr.siteid AND matrectrans.issuetype='RECEIPT' AND matrectrans.status = 'COMP'
LEFT JOIN prstatus prstatuswappr ON prstatuswappr.prnum = pr.prnum AND prstatuswappr.status = 'WAPPR' AND prstatuswappr.siteid = pr.siteid
LEFT JOIN prstatus prstatusappr ON prstatusappr.prnum = pr.prnum AND prstatusappr.status = 'APPR' AND prstatusappr.siteid = pr.siteid
where prline.itemnum is not null;

Answer 1

You may try doing an UPDATE with a CASE expression, something like this:

UPDATE yourTable
SET Column3 = CASE WHEN Column1 = 'Approved' THEN Column2 ELSE NULL END;