org.apache.tajo.plan.nameresolver

Enum NameResolvingMode

java.lang.Object

java.lang.Enum<NameResolvingMode>

org.apache.tajo.plan.nameresolver.NameResolvingMode

All Implemented Interfaces:

Serializable, Comparable<NameResolvingMode>

public enum NameResolvingMode
extends Enum<NameResolvingMode>

Motivation

Please take a look at the following example query:

   select (l_orderkey + l_orderkey) l_orderkey from lineitem where l_orderkey > 2 order by l_orderkey;
 

Although l_orderkey seems to be ambiguous, the above usages are available in commercial DBMSs. In order to eliminate the ambiguity, Tajo follows the behaviors of PostgreSQL.

Resolving Modes

From the behaviors of PostgreSQL, we found that there are three kinds of name resolving modes. Each definition is as follows:

• RELS_ONLY finds a column from the relations in the current block.
• RELS_AND_SUBEXPRS finds a column from the all relations in the current block and from aliased temporal fields; a temporal field means an explicitly aliased expression. If there are duplicated columns in the relation and temporal fields, this level firstly chooses the field in a relation.
• SUBEXPRS_AND_RELS is very similar to RELS_AND_SUBEXPRS. The main difference is that it firstly chooses an aliased temporal field instead of the fields in a relation.

The relationship between resolving modes and operators

• fields in select list and LIMIT are resolved in the REL_ONLY mode.
• fields in WHERE clause are resolved in the RELS_AND_SUBEXPRS mode.
• fields in GROUP BY, HAVING, and ORDER BY are resolved in the SUBEXPRS_AND_RELS mode.

Example

Please revisit the aforementioned example:

   select (l_orderkey + l_orderkey) l_orderkey from lineitem where l_orderkey > 2 order by l_orderkey;
 

With the above rules and the relationship between modes and operators, we can easily identify which reference points to which field.

1. l_orderkey included in (l_orderkey + l_orderkey) points to the field in the relation lineitem.
2. l_orderkey included in WHERE clause also points to the field in the relation lineitem.
3. l_orderkey included in ORDER BY clause points to the temporal field (l_orderkey + l_orderkey).

Enum Constant Summary

Enum Constants

Enum Constant and Description
LEGACY
RELS_AND_SUBEXPRS
RELS_ONLY
SUBEXPRS_AND_RELS

Method Summary

Methods

Modifier and Type	Method and Description
static NameResolvingMode	valueOf(String name) Returns the enum constant of this type with the specified name.
static NameResolvingMode[]	values() Returns an array containing the constants of this enum type, in the order they are declared.

Methods inherited from class java.lang.Enum

clone, compareTo, equals, finalize, getDeclaringClass, hashCode, name, ordinal, toString, valueOf

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Enum Constant Detail

RELS_ONLY

public static final NameResolvingMode RELS_ONLY

RELS_AND_SUBEXPRS

public static final NameResolvingMode RELS_AND_SUBEXPRS

SUBEXPRS_AND_RELS

public static final NameResolvingMode SUBEXPRS_AND_RELS

LEGACY

public static final NameResolvingMode LEGACY

Method Detail

values

public static NameResolvingMode[] values()

Returns an array containing the constants of this enum type, in the order they are declared. This method may be used to iterate over the constants as follows:

for (NameResolvingMode c : NameResolvingMode.values())
    System.out.println(c);

Returns:

an array containing the constants of this enum type, in the order they are declared

valueOf

public static NameResolvingMode valueOf(String name)

Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)

Parameters:

name - the name of the enum constant to be returned.

Returns:

the enum constant with the specified name

Throws:

IllegalArgumentException - if this enum type has no constant with the specified name

NullPointerException - if the argument is null