[GitHub] [calcite] tjbanghart commented on a diff in pull request #3034: [CALCITE-5357] Implement BigQuery FORMAT_TIMESTAMP, FORMAT_DATE, FORMAT_TIME, and FORMAT_DATETIME

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tjbanghart commented on code in PR #3034:
URL: https://github.com/apache/calcite/pull/3034#discussion_r1073950252


##########
core/src/main/java/org/apache/calcite/sql/dialect/MysqlSqlDialect.java:
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@@ -184,6 +185,46 @@ public MysqlSqlDialect(Context context) {
     return super.getCastSpec(type);
   }
 
+  /** {@inheritDoc}
+   *
+   * <p>MySQL format element reference:
+   * <a href="https://dev.mysql.com/doc/refman/8.0/en/date-and-time-functions.html#function_date-format">
+   * MySQL Date and Time Functions</a>.
+   */
+  @Override public String getFormatElement(FormatElementEnum fmtElement) {

Review Comment:
   Each dialect might have a different set of elements to represent the same type of datetime unit. 
   
   For example an abbreviated month name like `Jan` is `%b` in MySQL and `MON` in Snowflake. Each `SqlDialect` will have to override this method to supply the correct string for the element type. I only did MySQL, BigQuery, and Snowflake in the first commit because I wanted to get some feedback before working on each dialect.
   
   Oracle's format elements were chosen as the "base" set since they map closely to the SQL:2016 standard as described in [CALCITE-2980](https://issues.apache.org/jira/browse/CALCITE-2980).



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