Bug#52520 Difference in tinytext utf column metadata

      Problems:
      - regression (compating to version 5.1) in metadata for BLOB types
      - inconsistency between length metadata in server and embedded for BLOB types
      - wrong max_length calculation in items derived from BLOB columns
     @ libmysqld/lib_sql.cc
        Calculating length metadata in embedded similary to server version,
        using new function char_to_byte_length_safe().
     @ mysql-test/r/ctype_utf16.result
        Adding tests
     @ mysql-test/r/ctype_utf32.result
        Adding tests
     @ mysql-test/r/ctype_utf8.result
        Adding tests
     @ mysql-test/r/ctype_utf8mb4.result
        Adding tests
     @ mysql-test/t/ctype_utf16.test
        Adding tests
     @ mysql-test/t/ctype_utf32.test
        Adding tests
     @ mysql-test/t/ctype_utf8.test
        Adding tests
     @ mysql-test/t/ctype_utf8mb4.test
        Adding tests
     @ sql/field.cc
        Overriding char_length() for Field_blob:
        unlike in generic Item::char_length() we don't
        divide to mbmaxlen for BLOBs.
     @ sql/field.h
        - Making Field::char_length() virtual
        - Adding prototype for Field_blob::char_length()
     @ sql/item.h
        - Adding new helper function char_to_byte_length_safe()
        - Using new function
     @ sql/protocol.cc
        Using new function char_to_byte_length_safe().

    modified:
      libmysqld/lib_sql.cc
      mysql-test/r/ctype_utf16.result
      mysql-test/r/ctype_utf32.result
      mysql-test/r/ctype_utf8.result
      mysql-test/r/ctype_utf8mb4.result
      mysql-test/t/ctype_utf16.test
      mysql-test/t/ctype_utf32.test
      mysql-test/t/ctype_utf8.test
      mysql-test/t/ctype_utf8mb4.test
      sql/field.cc
      sql/field.h
      sql/item.h
      sql/protocol.cc

1 files changed, 33 insertions, 0 deletions

diff --git a/sql/field.cc b/sql/field.cc
index ee7d91c1fb6..ac40ae53d7c 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -9957,6 +9957,39 @@ Create_field::Create_field(Field *old_field,Field *orig_field)
 
 
 /**
+  maximum possible character length for blob.
+  
+  This method is used in Item_field::set_field to calculate
+  max_length for Item.
+  
+  For example:
+    CREATE TABLE t2 SELECT CONCAT(tinyblob_utf8_column) FROM t1;
+  must create a "VARCHAR(255) CHARACTER SET utf8" column.
+  
+  @return
+    length
+*/
+
+uint32 Field_blob::char_length()
+{
+  switch (packlength)
+  {
+  case 1:
+    return 255;
+  case 2:
+    return 65535;
+  case 3:
+    return 16777215;
+  case 4:
+    return (uint32) 4294967295U;
+  default:
+    DBUG_ASSERT(0); // we should never go here
+    return 0;
+  }
+}
+
+
+/**
   maximum possible display length for blob.
 
   @return