asolimando commented on a change in pull request #2230:
URL: https://github.com/apache/calcite/pull/2230#discussion_r512594390
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File path: core/src/main/java/org/apache/calcite/sql/fun/SqlItemOperator.java
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@@ -115,7 +115,8 @@ private SqlSingleOperandTypeChecker
getChecker(SqlCallBinding callBinding) {
@Override public String getAllowedSignatures(String name) {
return "<ARRAY>[<INTEGER>]\n"
- + "<MAP>[<VALUE>]";
+ + "<MAP>[<VALUE>]\n"
+ + "<ROW>[<CHARACTER>|<INTEGER>]";
}
Review comment:
`<MAP>[< CHARACTER >]` is only correct when we have a `MAP<CHARACTER,
_>` collection, which is not always the case.
That signature is static, so the concrete type is not known, the best we can
do is to use a "placeholder" for the right type, being it `<VALUE>` or `<KEY>`
or something else.
To make it clearer, consider that we could legally write a query like
`select map_field[select ...] ...`, provided that the inner `select ...`
returns an expression of type `K`, for a `map_field` of type `MAP<K, _>`.
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