yaooqinn opened a new pull request #26833: [WIP][SPARK-30203][SQL] store assignable if there is an appropriate user-defined cast function URL: https://github.com/apache/spark/pull/26833 … ### What changes were proposed in this pull request? #### 9.2 Store assignment ##### Syntax Rules 1) Let T be the TARGET and let V be the VALUE in an application of the Syntax Rules of this Subclause. 2) Let TD and SD be the declared types of T and V, respectively. **3) If TD is character string, binary string, numeric, boolean, datetime, interval, or a user-defined type, then either SD shall be assignable to TD or there shall exist an appropriate user-defined cast function UDCF from SD to TD.** _NOTE 319 — “Appropriate user-defined cast function” is defined in Subclause 4.11, “Data conversions”_ #### 4.11 Data conversions Implicit type conversion can occur in expressions, fetch operations, single row select operations, inserts, deletes, and updates. Explicit type conversions can be specified by the use of the CAST operator. The current implementation for ANSI store assignment is totally out of context. According to this rule, `there shall exist an appropriate user-defined cast function UDCF`, the spark legacy store assignment is just fine because we do have **appropriate cast functions**. At least according to the ansi cast rule, the current ANSI assignment policy is too strict to the ANSI cast rules ```scala * (SD) --------------------- (TD) ------------------------- * | EN AN C D T TS YM DT BO UDT B RT CT RW * EN | Y Y Y N N N M M N M N M N N * AN | Y Y Y N N N N N N M N M N N * C | Y Y Y Y Y Y Y Y Y M N M N N * D | N N Y Y N Y N N N M N M N N * T | N N Y N Y Y N N N M N M N N * TS | N N Y Y Y Y N N N M N M N N * YM | M N Y N N N Y N N M N M N N * DT | M N Y N N N N Y N M N M N N * BO | N N Y N N N N N Y M N M N N * UDT | M M M M M M M M M M M M M N * B | N N N N N N N N N M Y M N N * RT | M M M M M M M M M M M M N N * CT | N N N N N N N N N M N N M N * RW | N N N N N N N N N N N N N M * * Where: * EN = Exact Numeric * AN = Approximate Numeric * C = Character (Fixed- or Variable-Length, or Character Large Object) * D = Date * T = Time * TS = Timestamp * YM = Year-Month Interval * DT = Day-Time Interval * BO = Boolean * UDT = User-Defined Type * B = Binary (Fixed- or Variable-Length or Binary Large Object) * RT = Reference type * CT = Collection type * RW = Row type ``` ### Why are the changes needed? the current ansi store assignment rule is not ansi. ### Does this PR introduce any user-facing change? yes, pending ### How was this patch tested? <!-- If tests were added, say they were added here. Please make sure to add some test cases that check the changes thoroughly including negative and positive cases if possible. If it was tested in a way different from regular unit tests, please clarify how you tested step by step, ideally copy and paste-able, so that other reviewers can test and check, and descendants can verify in the future. If tests were not added, please describe why they were not added and/or why it was difficult to add. --> add uts.
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