added simple where conditions

main.go

@@ -0,0 +1,24 @@
+package main
+
+import "strings"
+
+func main() {
+	query := "select id, name from employees where department_id = 3 and salary > 10"
+	println(query)
+	r := strings.NewReader(query)
+
+	parser := NewParser(r)
+
+	stmt, err := parser.Parse()
+	if err != nil {
+		println(err.Error())
+	}
+
+	println(stmt.TableName)
+	for _, field := range stmt.Fields {
+		println(field)
+	}
+	for _, condition := range stmt.Conditions {
+		println(condition)
+	}
+}

parser.go

@@ -1,4 +1,4 @@
-package sql
+package main
 
 import (
 	"fmt"
@@ -7,8 +7,9 @@ import (
 
 // SelectStatement represents a SQL SELECT statement.
 type SelectStatement struct {
-	Fields    []string
-	TableName string
+	Fields     []string
+	TableName  string
+	Conditions []string
 }
 
 // Parser represents a parser.
@@ -63,6 +64,33 @@ func (p *Parser) Parse() (*SelectStatement, error) {
 	}
 	stmt.TableName = lit
 
+	// Next we should see the "WHERE" keyword.
+	if tok, lit := p.scanIgnoreWhitespace(); tok != WHERE {
+		return nil, fmt.Errorf("found %q, expected WHERE", lit)
+	}
+
+	// Next we should loop over all our and delimited conditions.
+	condition := ""
+	for {
+		// Read a field.
+		_, lit := p.scanIgnoreWhitespace()
+		condition += lit
+
+		if tok, lit := p.scanIgnoreWhitespace(); tok == AND {
+			stmt.Conditions = append(stmt.Conditions, condition)
+			condition = ""
+		} else {
+			if tok == EOF {
+				stmt.Conditions = append(stmt.Conditions, condition)
+				p.unscan()
+				break
+			} else {
+				condition += lit
+			}
+
+		}
+	}
+
 	// Return the successfully parsed statement.
 	return stmt, nil
 }

parser_test.go

@@ -1,4 +1,4 @@
-package sql_test
+package main
 
 import (
 	"reflect"

scanner.go

@@ -1,4 +1,4 @@
-package sql
+package main
 
 import (
 	"bufio"
@@ -35,6 +35,12 @@ func (s *Scanner) Scan() (tok Token, lit string) {
 
 	// Otherwise read the individual character.
 	switch ch {
+	case '=':
+		return OPER, string(ch)
+	case '>':
+		return OPER, string(ch)
+	case '<':
+		return OPER, string(ch)
 	case eof:
 		return EOF, ""
 	case '*':
@@ -93,6 +99,10 @@ func (s *Scanner) scanIdent() (tok Token, lit string) {
 		return SELECT, buf.String()
 	case "FROM":
 		return FROM, buf.String()
+	case "WHERE":
+		return WHERE, buf.String()
+	case "AND":
+		return AND, buf.String()
 	}
 
 	// Otherwise return as a regular identifier.
@@ -116,10 +126,15 @@ func (s *Scanner) unread() { _ = s.r.UnreadRune() }
 func isWhitespace(ch rune) bool { return ch == ' ' || ch == '\t' || ch == '\n' }
 
 // isLetter returns true if the rune is a letter.
-func isLetter(ch rune) bool { return (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') }
+func isLetter(ch rune) bool {
+	return (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') //|| isOpers(ch)
+}
 
 // isDigit returns true if the rune is a digit.
 func isDigit(ch rune) bool { return (ch >= '0' && ch <= '9') }
 
+// isOpers returns true if the rune is a digit.
+func isOpers(ch rune) bool { return ch == '=' || ch == '>' || ch == '<' }
+
 // eof represents a marker rune for the end of the reader.
 var eof = rune(0)

scanner_test.go

@@ -1,4 +1,4 @@
-package sql_test
+package main
 
 import (
 	"strings"

token.go

@@ -1,4 +1,4 @@
-package sql
+package main
 
 // Token represents a lexical token.
 type Token int
@@ -19,4 +19,7 @@ const (
 	// Keywords
 	SELECT
 	FROM
+	WHERE
+	AND // and
+	OPER
 )