MDEV-20732 Correctly set the length of the FORMAT() result for float data type as argument.

mysql-test/main/func_math.result

@@ -2723,6 +2723,22 @@ t2	CREATE TABLE `t2` (
   `c1` varchar(30) DEFAULT NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 DROP TABLE t1,t2;
+CREATE OR REPLACE TABLE t1 (f float);
+INSERT INTO t1 VALUES (3e38), (-3e38), (0), (12.34), (-12.34);
+CREATE OR REPLACE TABLE t2 AS SELECT FORMAT(f,0) FROM t1;
+SELECT * FROM t2;
+FORMAT(f,0)
+300,000,000,549,775,580,000,000,000,000,000,000,000
+-300,000,000,549,775,580,000,000,000,000,000,000,000
+0
+12
+-12
+SHOW CREATE TABLE t2;
+Table	Create Table
+t2	CREATE TABLE `t2` (
+  `FORMAT(f,0)` varchar(53) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+DROP TABLE t1,t2;
 #
 # End of 10.4 tests
 #

mysql-test/main/func_math.test

@@ -1733,6 +1733,13 @@ SELECT HEX(c1) FROM t2;
 SHOW CREATE TABLE t2;
 DROP TABLE t1,t2;
 
+CREATE OR REPLACE TABLE t1 (f float);
+INSERT INTO t1 VALUES (3e38), (-3e38), (0), (12.34), (-12.34);
+CREATE OR REPLACE TABLE t2 AS SELECT FORMAT(f,0) FROM t1;
+SELECT * FROM t2;
+SHOW CREATE TABLE t2;
+DROP TABLE t1,t2;
+
 --echo #
 --echo # End of 10.4 tests
 --echo #

mysql-test/main/func_str.result

@@ -2708,7 +2708,7 @@ create table t1(a float);
 insert into t1 values (1.33);
 select format(a, 2) from t1;
 Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
-def					format(a, 2)	253	4	4	Y	0	39	8
+def					format(a, 2)	253	56	4	Y	0	39	8
 format(a, 2)
 1.33
 drop table t1;

sql/item_strfunc.cc

@@ -2668,11 +2668,10 @@ bool Item_func_format::fix_length_and_dec()
 {
   uint32 char_length= args[0]->type_handler()->Item_decimal_notation_int_digits(args[0]);
   uint dec= FORMAT_MAX_DECIMALS;
-  if (args[1]->const_item() && !args[1]->is_expensive())
+  if (args[1]->const_item() && !args[1]->is_expensive() && !args[1]->null_value)
   {
     Longlong_hybrid tmp= args[1]->to_longlong_hybrid();
-    if (!args[1]->null_value)
-      dec= tmp.to_uint(FORMAT_MAX_DECIMALS);
+    dec= tmp.to_uint(FORMAT_MAX_DECIMALS);
   }
   uint32 max_sep_count= (char_length / 3) + (dec ? 1 : 0) + /*sign*/1;
   collation.set(default_charset());

sql/sql_type.cc

@@ -3550,7 +3550,7 @@ Type_handler_general_purpose_int::Item_decimal_notation_int_digits(
 /*************************************************************************/
 
 /*
-    Decimal to binary digits ratio converges to log2(10) thus using 3 as
+    Binary to Decimal digits ratio converges to log2(10) thus using 3 as
     a divisor.
 */
 uint32

sql/sql_type.h

@@ -5147,6 +5147,7 @@ class Type_handler_float: public Type_handler_real_result
   }
   bool type_can_have_auto_increment_attribute() const { return true; }
   uint32 max_display_length(const Item *item) const { return 25; }
+  uint32 Item_decimal_notation_int_digits(const Item *item) const { return 39; }
   uint32 calc_pack_length(uint32 length) const { return sizeof(float); }
   Item *create_typecast_item(THD *thd, Item *item,
                              const Type_cast_attributes &attr) const;