Parser and Expressions

Parser Specifications

The current parser must take in a string as input, and return a Expr* in a method with the following signature:

Expr *parseRowExpression(string input, DataType *inputDataTypes, int32_t veccount);

DataType is an enum which is defined in core/src/expression/expressions.h, and covers all the possible types for a column. These are: STRINGD, INT32D, INT64D, DOUBLED, BOOLD. The inputVecTypes array contains the type of each column in order, and there are veccount columns in total.

All the different kinds of Expr* are listed in core/src/expression/expressions.h. When parsing, each Expr* must have its dataType member set correctly (usually with the constructor for the Expr which takes in a data type. The different types of Expr are: DataExpr: Holds a piece of literal data or a column index. UnaryExpr: Represents a unary expression (such as NOT). BinaryExpr: Represents a binary expression (such as +, -, *, /, %, AND, OR, <, <=, >, >=, =, <>) InExpr: Represents an IN SQL operator. Holds a vector of arguments which are Expr*, and the first argument is the value to be compared to every other argument. BetweenExpr: Represents a BETWEEN SQL operator. Holds a value, lower bound, and upper bound, all of which are Expr*. IfExpr: Represents an SQL conditional. Holds a condition, an expression to be evaluated if the condition is true, and an expression to be evaluated if the condition is false; all of these are Expr*. CoalesceExpr: Represents an SQL COALESCE. Has a value 1 and a value 2. If value 1 has a null value then value 2 is returned, otherwise value 1 is returned. FuncExpr: Represents any function, whether internal or user-defined. Has a name and an argument vector of Expr*.

Using parserhelper

In core/src/expression/parserhelper.h and its corresponding .cpp file, there are a few methods to help with parsing.

DataType FuncRetTypeMap(string funcID, vector<Expr*> args);

The FuncRetTypeMap method takes in a function name funcID and a vector containing its arguments (which are all Expr*), and returns a DataType denoting the returned type of the function.

bool HasValidArguments(string funcID, vector<Expr*> args, bool checkTypes);

The HasValidArguments method checks whether or not a FuncExpr* (i.e. an expression representing a function call) is valid, in terms of whether the number of arguments match up with the function name. If true is passed to the checkTypes argument, then the types will be checked as well, although types will not be checked for external developer functions.