[MINOR] Add example for MAP type in reference docs

[chucheng92]

The background is that I was going to implement Spark's MAP function, and found that the MAP constructor embedded in calcite had no examples in docs. So try to add it here.

Background and context can be found at: https://issues.apache.org/jira/browse/CALCITE-5918

[mihaibudiu]

Is there a test which confirms this syntax?

[chucheng92]

Is there a test which confirms this syntax?

thanks for reviewing. Yes, we have.

calcite/testkit/src/main/java/org/apache/calcite/test/SqlOperatorTest.java

Line 10162 in aef9bdb

@Test void testMapValueConstructor() {

The background is that I was going to implement Spark's MAP function, and found that the MAP constructor embedded in calcite had no examples in docs. So try to add it here.

[LakeShen]

LGTM

[JiajunBernoulli]

This example is different from other examples.

I think the example should be map(varchar, int).

[chucheng92]

thanks. I have updated to map[varchar, int] instead of map(varchar, int), because the previous one is calcite standard form, the later one is Spark map form. We haven't implemented this yet. WDYT?

[JiajunBernoulli]

@chucheng92 Do you know generateTypeString? Please take a look at them.

• ArraySqlType#generateTypeString
• MapSqlType#generateTypeString
• MultisetSqlType#generateTypeString

[chucheng92]

@JiajunBernoulli thanks. Jiajun, I get your point. I actually wanted to add an example of map function at the beginning, here is actually map type.

I have updated the PR. thanks for reminding me.

[JiajunBernoulli]

@chucheng92
In fact, we have many map constructor examples.

calcite/core/src/test/resources/sql/misc.iq

Line 2346 in 6f79436

from (select map['a', false, 'b', true] from (values (2))) as t(mycol);

calcite/core/src/test/resources/sql/misc.iq

Line 2595 in 6f79436

map[multiset['A'], map[1,2], multiset['B'], map[3, 4]] as z

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[chucheng92]

hi,@JiajunBernoulli I have squashed the commit, If u have time, could you help to merge this?