* #3848 Fix regression for Sql Server and Oracle with exists() introduced in 18.2.0
Fix#3848: exists() generates invalid scalar SQL on SQL Server and Oracle
Query.exists() generated `select exists(<subquery>)`, which is valid on
Postgres/H2/MySQL but rejected by SQL Server and Oracle since both only
support EXISTS as a predicate, not as a directly selectable scalar boolean
expression. ┃
┃
Add DatabasePlatform.existsWithCaseWhen/existsFromClause capability flags
and use them in CQueryBuilder.wrapSelectExists() to generate
`select case when exists(<subquery>) then 1 else 0 end` on platforms that ┃
need it, with an additional ` from dual` suffix for Oracle (which requires ┃
a FROM clause on every select). CQueryExists reads the boolean result via ┃
ResultSet.getBoolean(1), which correctly interprets the resulting 0/1 int.
* Fix tests TestInsertCheckUnique for Oracle and SQL Server
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Co-authored-by: robin.bygrave <robin.bygrave@eroad.com>
* checkUniqueness supports queryCache and skipClean
* Keep the DB.checkUniqueness() as per original (not overload there)
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Co-authored-by: Roland Praml <roland.praml@foconis.de>
Noting that value() currently calls through to getValue() hence
this is no real change. This is done because value() is also
a public method Property.value() [and this should probably
change to use getValueIntercept() rather than getValue()]
