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Item_default_value Class Reference
Inheritance diagram for Item_default_value:
Item_field Item_ident Item

List of all members.

Public Member Functions

 Item_default_value (Name_resolution_context *context_arg)
 Item_default_value (Name_resolution_context *context_arg, Item *a)
enum Type type () const
bool eq (const Item *item, bool binary_cmp) const
bool fix_fields (THD *, Item **)
virtual void print (String *str, enum_query_type query_type)
type_conversion_status save_in_field (Field *field_arg, bool no_conversions)
table_map used_tables () const
Itemget_tmp_table_item (THD *thd)
bool walk (Item_processor processor, bool walk_subquery, uchar *args)
Itemtransform (Item_transformer transformer, uchar *args)

Public Attributes


Member Function Documentation

bool Item_default_value::eq ( const Item item,
bool  binary_cmp 
) const [virtual]

This function is called when:

  • Comparing items in the WHERE clause (when doing where optimization)
  • When trying to find an ORDER BY/GROUP BY item in the SELECT part
  • When matching fields in multiple equality objects (Item_equal)

Reimplemented from Item_field.

bool Item_default_value::fix_fields ( THD *  thd,
Item **  reference 
) [virtual]

Resolve the name of a column reference.

The method resolves the column reference represented by 'this' as a column present in one of: FROM clause, SELECT clause, GROUP BY clause of a query Q, or in outer queries that contain Q.

The name resolution algorithm used is (where [T_j] is an optional table name that qualifies the column name):

      search for a column or derived column named col_ref_i
      [in table T_j] in the FROM clause of Q;

      if such a column is NOT found AND    // Lookup in outer queries.
         there are outer queries
        for each outer query Q_k beginning from the inner-most one
          search for a column or derived column named col_ref_i
          [in table T_j] in the FROM clause of Q_k;

          if such a column is not found
            Search for a column or derived column named col_ref_i
            [in table T_j] in the SELECT and GROUP clauses of Q_k.

Notice that compared to Item_ref::fix_fields, here we first search the FROM clause, and then we search the SELECT and GROUP BY clauses.

[in]thdcurrent thread
[in,out]referenceview column if this item was resolved to a view column
Return values:
TRUEif error
FALSEon success

Reimplemented from Item_field.

void Item_default_value::print ( String str,
enum_query_type  query_type 
) [virtual]

This method is used for to:

  • to generate a view definition query (SELECT-statement);
  • to generate a SQL-query for EXPLAIN EXTENDED;
  • to generate a SQL-query to be shown in INFORMATION_SCHEMA;
  • debug.

For more information about view definition query, INFORMATION_SCHEMA query and why they should be generated from the Item-tree,

See also:

Reimplemented from Item_field.

type_conversion_status Item_default_value::save_in_field ( Field field,
bool  no_conversions 
) [virtual]

Save a temporal value in packed longlong format into a Field. Used in optimizer.

OUTfield The field to set the value to.
Return values:
0On success.
>0In error.

Reimplemented from Item_field.

Item * Item_default_value::transform ( Item_transformer  transformer,
uchar *  args 
) [virtual]

This method like the walk method traverses the item tree, but at the same time it can replace some nodes in the tree.

Reimplemented from Item.

The documentation for this class was generated from the following files:
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