SQL: Implement CONVERT, an alternative to CAST

`CONVERT` works exactly like cast with slightly different syntax:
`CONVERT(<value>, <data_type)` as opposed to `CAST(<value> AS <data_type>)`

Moreover it support format of the MS-SQL data types `SQL_<type>`,
e.g.: `SQL_INTEGER`

Closes: elastic#34513

docs/reference/sql/functions/type-conversion.asciidoc

@@ -19,7 +19,7 @@ CAST ( expression<1> AS data_type<2> )
 
 .Description
 
-Casts the result of the given expression to the target type.
+Casts the result of the given expression to the target <<sql-data-types, data type>>.
 If the cast is not possible (for example because of target type is too narrow or because
 the value itself cannot be converted), the query fails.
 
@@ -36,4 +36,33 @@ include-tagged::{sql-specs}/docs.csv-spec[conversionIntToStringCast]
 ["source","sql",subs="attributes,callouts,macros"]
 ----
 include-tagged::{sql-specs}/docs.csv-spec[conversionStringToDateCast]
-----
+----
+
+
+[[sql-functions-type-conversion-convert]]
+==== `CONVERT`
+
+.Synopsis
+[source, sql]
+----
+CONVERT ( expression<1>, data_type<2> )
+----
+
+<1> Expression to convert
+<2> Target data type to convert to
+
+.Description
+
+Works exactly like <<sql-functions-type-conversion-cast>> with slightly different syntax.
+Moreover, apart from the standard <<sql-data-types, data types>> it supports the corresponding
+https://docs.microsoft.com/en-us/sql/odbc/reference/appendixes/explicit-data-type-conversion-function?view=sql-server-2017[MS-SQL data types].
+
+["source","sql",subs="attributes,callouts,macros"]
+----
+include-tagged::{sql-specs}/docs.csv-spec[conversionStringToIntConvertMSSQLDataType]
+----
+
+["source","sql",subs="attributes,callouts,macros"]
+----
+include-tagged::{sql-specs}/docs.csv-spec[conversionStringToIntConvertESDataType]
+----

x-pack/plugin/sql/sql-proto/src/main/java/org/elasticsearch/xpack/sql/type/DataType.java

@@ -9,6 +9,7 @@
 import java.sql.SQLType;
 import java.sql.Timestamp;
 import java.util.Arrays;
+import java.util.HashMap;
 import java.util.Locale;
 import java.util.Map;
 import java.util.stream.Collectors;
@@ -44,12 +45,63 @@ public enum DataType {
     DATE(        JDBCType.TIMESTAMP, Timestamp.class, Long.BYTES,        24,                24);
     // @formatter:on
 
+    public static final String MSSQL_DATATYPE_PREFIX = "SQL_";
+
     private static final Map<SQLType, DataType> jdbcToEs;
+    private static final Map<String, DataType> mssqlToEs;
 
     static {
         jdbcToEs = Arrays.stream(DataType.values())
                 .filter(dataType -> dataType != TEXT && dataType != NESTED && dataType != SCALED_FLOAT) // Remove duplicates
                 .collect(Collectors.toMap(dataType -> dataType.jdbcType, dataType -> dataType));
+
+        mssqlToEs = new HashMap<>(36);
+
+        // Numeric
+        mssqlToEs.put("SQL_BIT", BOOLEAN);
+        mssqlToEs.put("SQL_TINYINT", BYTE);
+        mssqlToEs.put("SQL_SMALLINT", SHORT);
+        mssqlToEs.put("SQL_INTEGER", INTEGER);
+        mssqlToEs.put("SQL_BIGINT", LONG);
+        mssqlToEs.put("SQL_FLOAT", FLOAT);
+        mssqlToEs.put("SQL_REAL", FLOAT);
+        mssqlToEs.put("SQL_DOUBLE", DOUBLE);
+        mssqlToEs.put("SQL_DECIMAL", DOUBLE);
+        mssqlToEs.put("SQL_NUMERIC", DOUBLE);
+
+        // String
+        mssqlToEs.put("SQL_GUID", KEYWORD);
+        mssqlToEs.put("SQL_CHAR", KEYWORD);
+        mssqlToEs.put("SQL_WCHAR", KEYWORD);
+        mssqlToEs.put("SQL_VARCHAR", TEXT);
+        mssqlToEs.put("SQL_WVARCHAR", TEXT);
+        mssqlToEs.put("SQL_LONGVARCHAR", TEXT);
+        mssqlToEs.put("SQL_WLONGVARCHAR", TEXT);
+
+        // Binary
+        mssqlToEs.put("SQL_BINARY", BINARY);
+        mssqlToEs.put("SQL_VARBINARY", BINARY);
+        mssqlToEs.put("SQL_LONGVARBINARY", BINARY);
+
+        // Date
+        mssqlToEs.put("SQL_DATE", DATE);
+        mssqlToEs.put("SQL_TIME", DATE);
+        mssqlToEs.put("SQL_TIMESTAMP", DATE);
+
+        // Intervals - Currently Not Supported
+        mssqlToEs.put("SQL_INTERVAL_HOUR_TO_MINUTE", null);
+        mssqlToEs.put("SQL_INTERVAL_HOUR_TO_SECOND", null);
+        mssqlToEs.put("SQL_INTERVAL_MINUTE_TO_SECOND", null);
+        mssqlToEs.put("SQL_INTERVAL_MONTH", null);
+        mssqlToEs.put("SQL_INTERVAL_YEAR", null);
+        mssqlToEs.put("SQL_INTERVAL_YEAR_TO_MONTH", null);
+        mssqlToEs.put("SQL_INTERVAL_DAY", null);
+        mssqlToEs.put("SQL_INTERVAL_HOUR", null);
+        mssqlToEs.put("SQL_INTERVAL_MINUTE", null);
+        mssqlToEs.put("SQL_INTERVAL_SECOND", null);
+        mssqlToEs.put("SQL_INTERVAL_DAY_TO_HOUR", null);
+        mssqlToEs.put("SQL_INTERVAL_DAY_TO_MINUTE", null);
+        mssqlToEs.put("SQL_INTERVAL_DAY_TO_SECOND", null);
     }
 
     /**
@@ -162,6 +214,9 @@ public static Class<?> fromJdbcTypeToJava(SQLType jdbcType) {
         return jdbcToEs.get(jdbcType).javaClass();
     }
 
+    public static DataType fromMSSQLType(String mssqlType) {
+        return mssqlToEs.get(mssqlType);
+    }
     /**
      * Creates returns DataType enum coresponding to the specified es type
      * <p>
@@ -170,4 +225,4 @@ public static Class<?> fromJdbcTypeToJava(SQLType jdbcType) {
     public static DataType fromEsType(String esType) {
         return DataType.valueOf(esType.toUpperCase(Locale.ROOT));
     }
-}
+}

x-pack/plugin/sql/src/main/antlr/SqlBase.g4

@@ -226,14 +226,20 @@ primaryExpression
     ;
 
 castExpression
-    : castTemplate                                                                   
-    | FUNCTION_ESC castTemplate ESC_END                                              
+    : castTemplate
+    | FUNCTION_ESC castTemplate ESC_END
+    | convertTemplate
+    | FUNCTION_ESC convertTemplate ESC_END
     ;
 
 castTemplate
     : CAST '(' expression AS dataType ')'
     ;
-
+
+convertTemplate
+    : CONVERT '(' expression ',' dataType ')'
+    ;
+
 extractExpression
     : extractTemplate
     | FUNCTION_ESC extractTemplate ESC_END
@@ -347,6 +353,7 @@ CAST: 'CAST';
 CATALOG: 'CATALOG';
 CATALOGS: 'CATALOGS';
 COLUMNS: 'COLUMNS';
+CONVERT: 'CONVERT';
 DEBUG: 'DEBUG';
 DESC: 'DESC';
 DESCRIBE: 'DESCRIBE';