Add support for expressions in case

[tomershay]

MySQL supports expressions in CASE statements before the WHEN clause.
Example: CASE <expr> WHEN ....

The expression after the CASE keyword is optional.
This PR adds support for such expressions, in case they exist in the query.

Relevant docs for both options: https://dev.mysql.com/doc/refman/5.7/en/case.html

[coveralls]

Coverage decreased (-0.02%) to 83.438% when pulling 2e3d2b1 on tomershay:add_support_for_expressions_in_case into 430b3ee on JSQLParser:master.

[wumpz]

This expression right after case is supported a while. Your test sql is parsed using an unmodified JSqlParser V3.2-SNAPSHOT:

String sqls = "SELECT a FROM tbl1 LEFT JOIN tbl2 ON CASE tbl1.col1 WHEN tbl1.col1 = 1 THEN tbl1.col2 = tbl2.col2 ELSE tbl1.col3 = tbl2.col3 END";

So maybe you had another problem?

Here are the issues, that solved and extended your kind of syntax:

#371, #862

at least the older one is from dec 2016.

[tomershay]

Maybe I'm missing something, but I just built the latest master from source, and the following test fails:

public void testExpressionsInCaseBeforeWhen() throws JSQLParserException {
    assertSqlCanBeParsedAndDeparsed("SELECT a FROM tbl1 LEFT JOIN tbl2 ON CASE tbl1.col1 WHEN tbl1.col1 = 1 THEN tbl1.col2 = tbl2.col2 ELSE tbl1.col3 = tbl2.col3 END");
}

The error:

net.sf.jsqlparser.JSQLParserException
	at net.sf.jsqlparser.parser.CCJSqlParserUtil.parse(CCJSqlParserUtil.java:65)
	at net.sf.jsqlparser.test.TestUtils.assertSqlCanBeParsedAndDeparsed(TestUtils.java:57)
	at net.sf.jsqlparser.test.TestUtils.assertSqlCanBeParsedAndDeparsed(TestUtils.java:53)
	at net.sf.jsqlparser.test.TestUtils.assertSqlCanBeParsedAndDeparsed(TestUtils.java:41)
	at net.sf.jsqlparser.statement.select.SelectTest.testExpressionsInCaseBeforeWhen(SelectTest.java:1307)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
	at org.junit.rules.TestWatcher$1.evaluate(TestWatcher.java:55)
	at org.junit.rules.RunRules.evaluate(RunRules.java:20)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
	at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
Caused by: net.sf.jsqlparser.parser.ParseException: Encountered unexpected token: "CASE" "CASE"
    at line 1, column 38.

Was expecting one of:

    "!"
    "("
    "NOT"

	at net.sf.jsqlparser.parser.CCJSqlParser.generateParseException(CCJSqlParser.java:22874)
	at net.sf.jsqlparser.parser.CCJSqlParser.jj_consume_token(CCJSqlParser.java:22721)
	at net.sf.jsqlparser.parser.CCJSqlParser.AndExpression(CCJSqlParser.java:7552)
	at net.sf.jsqlparser.parser.CCJSqlParser.OrExpression(CCJSqlParser.java:7492)
	at net.sf.jsqlparser.parser.CCJSqlParser.Expression(CCJSqlParser.java:7463)
	at net.sf.jsqlparser.parser.CCJSqlParser.JoinerExpression(CCJSqlParser.java:6274)
	at net.sf.jsqlparser.parser.CCJSqlParser.JoinsList(CCJSqlParser.java:6081)
	at net.sf.jsqlparser.parser.CCJSqlParser.PlainSelect(CCJSqlParser.java:3746)
	at net.sf.jsqlparser.parser.CCJSqlParser.SetOperationList(CCJSqlParser.java:3954)
	at net.sf.jsqlparser.parser.CCJSqlParser.SelectBody(CCJSqlParser.java:3613)
	at net.sf.jsqlparser.parser.CCJSqlParser.Select(CCJSqlParser.java:3606)
	at net.sf.jsqlparser.parser.CCJSqlParser.SingleStatement(CCJSqlParser.java:124)
	at net.sf.jsqlparser.parser.CCJSqlParser.Statement(CCJSqlParser.java:75)
	at net.sf.jsqlparser.parser.CCJSqlParserUtil.parse(CCJSqlParserUtil.java:63)
	... 29 more
Caused by:
net.sf.jsqlparser.parser.ParseException: Encountered unexpected token: "CASE" "CASE"
    at line 1, column 38.

[tomershay]

It seems that the source code might indicate the problem:

<K_CASE>
    (
            ( clause=WhenThenSearchCondition() { whenClauses.add(clause); } )+
        |
            switchExp=Condition()
             ( clause=WhenThenValue() { whenClauses.add(clause); } )+
    )

From what I understand, the expression-after-case is currently supported when it has a simple expression following it (handled by WhenThenValue).
I believe that the issue I ran into with the query sample I mentioned, is that the WHEN/THEN includes a more complex expression (i.e., equality condition), which should be handled by WhenThenSearchCondition, but in that case, the expression-after-case isn't allowed by the existing template.
So is switchExp actually there to represent the expression after the CASE keyword?
If that's the case, I can try to fix the pull request and fix the code accordingly to support the use case I'm describing.
Please share your thoughts.

[wumpz]

That is right. switchExp represents exactly the expression after CASE. Strangely enough, here I am not anymore able to parse your test statement, but I have no actual sources at hand. Maybe some of my last not yet pushed changes did have this effect. I have to look into this.

[tomershay]

Thanks for the update. Please let me know if a fix for this is coming up in your internal changes. If not, let me know what you think we should change in this PR to make it valuable and approvable.

[wumpz]

I don't know what I saw :(. Now it fails here as well. However, I changed it to accept your case as well. Indeed the whole case parsing was simplified because there is no more difference between both cases.

Just wait a bit. I have another issue to close. JSqlParser here would fail some tests and I do not yet want to push this version.

[wumpz]

I just deployed a new version. Could you check it?

[tomershay]

@wumpz, just tested it and it works great!
Thanks!