Update all values of a column in a table to be equal to the values of a column in another table.

The database uses db2, which has two tables: Check table (STUDY_TBL) and filter table (SELECTION_TBL)

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The description of STUDY_TBL is roughly as follows:

STUDY_LID integer primary key,

STUDY_DATE DATE

......

The definition of SELECTION_TBL is roughly as follows:

SELECTION_LID integer primary key,

STUDY_LID INTEGER,

STUDY_DATE

......

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STUDY_LID is not unique in SELECTION_TBL. Now we want to update all STUDY_DATE in SELECTION_TBL to be the same as STUDY_DATE in STUDY_TBL (that is, in the two tables, STUDY _ and LID are the same, STUDY_DATE in SELECTION_TBL must be the same as STUDY_DATE in STUDY_TBL ).

The SQL statement is as follows:

Update pacs. SELECTION_TBL SEL
SET STUDY_DATE = (select st. STUDY_DATE
From pacs. STUDY_TBL ST
Where st. STUDY_LID = SEL. STUDY_LID)
WHERE EXISTS
(SELECT 1 from pacs. STUDY_TBL ST1 WHERE ST1.STUDY _ LID = SEL. STUDY_LID)

PACS is the mode name. We will discuss the usage of exists in detail in future articles ....