Class SqlHint

All Implemented Interfaces:

public class SqlHint extends SqlCall
A SqlHint is a node of a parse tree which represents a sql hint expression.

Basic hint grammar is: hint_name[(option1, option2 ...)]. The hint_name should be a simple identifier, the options part is optional. Every option can be of four formats:

  • simple identifier
  • literal
  • key value pair whose key is a simple identifier and value is a string literal
  • key value pair whose key and value are both string literal

The option format can not be mixed in, they should either be all simple identifiers or all literals or all key value pairs.

We support 2 kinds of hints in the parser:

  • Query hint, right after the select keyword, i.e.:
         select /*+ hint1, hint2, ... */ ...
  • Table hint: right after the referenced table name, i.e.:
         select f0, f1, f2 from t1 /*+ hint1, hint2, ... */ ...
  • Constructor Details

  • Method Details

    • getOperator

      public SqlOperator getOperator()
      Specified by:
      getOperator in class SqlCall
    • getOperandList

      public List<SqlNode> getOperandList()
      Description copied from class: SqlCall
      Returns the list of operands. The set and order of operands is call-specific.

      Note: the proper type would be List<@Nullable SqlNode>, however, it would trigger too many changes to the current codebase.

      Specified by:
      getOperandList in class SqlCall
      the list of call operands, never null, the operands can be null
    • getName

      public String getName()
      Returns the sql hint name.
    • getOptionFormat

      public SqlHint.HintOptionFormat getOptionFormat()
      Returns the hint option format.
    • getOptionList

      public List<String> getOptionList()
      Returns a string list if the hint option is a list of simple SQL identifier, or a list of literals, else returns an empty list.
    • getOptionKVPairs

      public Map<String,String> getOptionKVPairs()
      Returns a key value string map if the hint option is a list of pair, each pair contains a simple SQL identifier and a string literal; else returns an empty map.
    • unparse

      public void unparse(SqlWriter writer, int leftPrec, int rightPrec)
      Description copied from class: SqlNode
      Writes a SQL representation of this node to a writer.

      The leftPrec and rightPrec parameters give us enough context to decide whether we need to enclose the expression in parentheses. For example, we need parentheses around "2 + 3" if preceded by "5 *". This is because the precedence of the "*" operator is greater than the precedence of the "+" operator.

      The algorithm handles left- and right-associative operators by giving them slightly different left- and right-precedence.

      If SqlWriter.isAlwaysUseParentheses() is true, we use parentheses even when they are not required by the precedence rules.

      For the details of this algorithm, see SqlCall.unparse(org.apache.calcite.sql.SqlWriter, int, int).

      unparse in class SqlCall
      writer - Target writer
      leftPrec - The precedence of the SqlNode immediately preceding this node in a depth-first scan of the parse tree
      rightPrec - The precedence of the SqlNode immediately