diff --git a/internal/jet/dialect.go b/internal/jet/dialect.go
index 71720d1..acf03d9 100644
--- a/internal/jet/dialect.go
+++ b/internal/jet/dialect.go
@@ -14,7 +14,7 @@ type Dialect interface {
 // SerializerFunc func
 type SerializerFunc func(statement StatementType, out *SQLBuilder, options ...SerializeOption)
 
-//// SerializeOverride func
+// SerializeOverride func
 type SerializeOverride func(expressions ...Serializer) SerializerFunc
 
 // QueryPlaceholderFunc func
diff --git a/internal/jet/expression.go b/internal/jet/expression.go
index 379bd70..26b9186 100644
--- a/internal/jet/expression.go
+++ b/internal/jet/expression.go
@@ -8,25 +8,26 @@ type Expression interface {
 	GroupByClause
 	OrderByClause
 
-	// Test expression whether it is a NULL value.
+	// IS_NULL tests expression whether it is a NULL value.
 	IS_NULL() BoolExpression
-	// Test expression whether it is a non-NULL value.
+	// IS_NOT_NULL tests expression whether it is a non-NULL value.
 	IS_NOT_NULL() BoolExpression
 
-	// Check if this expressions matches any in expressions list
+	// IN checks if this expressions matches any in expressions list
 	IN(expressions ...Expression) BoolExpression
-	// Check if this expressions is different of all expressions in expressions list
+	// NOT_IN checks if this expressions is different of all expressions in expressions list
 	NOT_IN(expressions ...Expression) BoolExpression
 
-	// The temporary alias name to assign to the expression
+	// AS the temporary alias name to assign to the expression
 	AS(alias string) Projection
 
-	// Expression will be used to sort query result in ascending order
+	// ASC expression will be used to sort query result in ascending order
 	ASC() OrderByClause
-	// Expression will be used to sort query result in ascending order
+	// DESC expression will be used to sort query result in ascending order
 	DESC() OrderByClause
 }
 
+// ExpressionInterfaceImpl implements Expression interface methods
 type ExpressionInterfaceImpl struct {
 	Parent Expression
 }
@@ -35,30 +36,37 @@ func (e *ExpressionInterfaceImpl) fromImpl(subQuery SelectTable) Projection {
 	return e.Parent
 }
 
+// IS_NULL tests expression whether it is a NULL value.
 func (e *ExpressionInterfaceImpl) IS_NULL() BoolExpression {
 	return newPostfixBoolOperatorExpression(e.Parent, "IS NULL")
 }
 
+// IS_NOT_NULL tests expression whether it is a non-NULL value.
 func (e *ExpressionInterfaceImpl) IS_NOT_NULL() BoolExpression {
 	return newPostfixBoolOperatorExpression(e.Parent, "IS NOT NULL")
 }
 
+// IN checks if this expressions matches any in expressions list
 func (e *ExpressionInterfaceImpl) IN(expressions ...Expression) BoolExpression {
 	return newBinaryBoolOperatorExpression(e.Parent, WRAP(expressions...), "IN")
 }
 
+// NOT_IN checks if this expressions is different of all expressions in expressions list
 func (e *ExpressionInterfaceImpl) NOT_IN(expressions ...Expression) BoolExpression {
 	return newBinaryBoolOperatorExpression(e.Parent, WRAP(expressions...), "NOT IN")
 }
 
+// AS the temporary alias name to assign to the expression
 func (e *ExpressionInterfaceImpl) AS(alias string) Projection {
 	return newAlias(e.Parent, alias)
 }
 
+// ASC expression will be used to sort query result in ascending order
 func (e *ExpressionInterfaceImpl) ASC() OrderByClause {
 	return newOrderByClause(e.Parent, true)
 }
 
+// DESC expression will be used to sort query result in ascending order
 func (e *ExpressionInterfaceImpl) DESC() OrderByClause {
 	return newOrderByClause(e.Parent, false)
 }
diff --git a/internal/jet/interval.go b/internal/jet/interval.go
index 705f2be..e66ca56 100644
--- a/internal/jet/interval.go
+++ b/internal/jet/interval.go
@@ -1,14 +1,17 @@
 package jet
 
+// Interval is internal common representation of sql interval
 type Interval interface {
 	Serializer
 	IsInterval
 }
 
+// IsInterval interface
 type IsInterval interface {
 	isInterval()
 }
 
+// NewInterval creates new interval from serializer
 func NewInterval(s Serializer) Interval {
 	newInterval := &intervalImpl{
 		interval: s,
diff --git a/internal/jet/literal_expression.go b/internal/jet/literal_expression.go
index 6983b8f..499b7b4 100644
--- a/internal/jet/literal_expression.go
+++ b/internal/jet/literal_expression.go
@@ -334,20 +334,20 @@ func WRAP(expression ...Expression) Expression {
 
 //---------------------------------------------------//
 
-type RawExpression struct {
+type rawExpression struct {
 	ExpressionInterfaceImpl
 
 	Raw string
 }
 
-func (n *RawExpression) serialize(statement StatementType, out *SQLBuilder, options ...SerializeOption) {
+func (n *rawExpression) serialize(statement StatementType, out *SQLBuilder, options ...SerializeOption) {
 	out.WriteString(n.Raw)
 }
 
 // Raw can be used for any unsupported functions, operators or expressions.
 // For example: Raw("current_database()")
 func Raw(raw string) Expression {
-	rawExp := &RawExpression{Raw: raw}
+	rawExp := &rawExpression{Raw: raw}
 	rawExp.ExpressionInterfaceImpl.Parent = rawExp
 
 	return rawExp
diff --git a/internal/jet/serializer.go b/internal/jet/serializer.go
index d5ff4b9..dc661d7 100644
--- a/internal/jet/serializer.go
+++ b/internal/jet/serializer.go
@@ -42,6 +42,7 @@ func contains(options []SerializeOption, option SerializeOption) bool {
 	return false
 }
 
+// ListSerializer serializes list of serializers with separator
 type ListSerializer struct {
 	Serializers []Serializer
 	Separator   string
diff --git a/internal/jet/sql_builder.go b/internal/jet/sql_builder.go
index 3b34ab2..95bd0b6 100644
--- a/internal/jet/sql_builder.go
+++ b/internal/jet/sql_builder.go
@@ -142,12 +142,8 @@ func argToString(value interface{}) string {
 			return "TRUE"
 		}
 		return "FALSE"
-	case int:
-		return strconv.FormatInt(int64(bindVal), 10)
-	case int32:
-		return strconv.FormatInt(int64(bindVal), 10)
-	case int64:
-		return strconv.FormatInt(bindVal, 10)
+	case int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64:
+		return integerTypesToString(bindVal)
 
 	case float32:
 		return strconv.FormatFloat(float64(bindVal), 'f', -1, 64)
@@ -167,6 +163,33 @@ func argToString(value interface{}) string {
 	}
 }
 
+func integerTypesToString(value interface{}) string {
+	switch bindVal := value.(type) {
+	case bool:
+	case int:
+		return strconv.FormatInt(int64(bindVal), 10)
+	case uint:
+		return strconv.FormatUint(uint64(bindVal), 10)
+	case int8:
+		return strconv.FormatInt(int64(bindVal), 10)
+	case uint8:
+		return strconv.FormatUint(uint64(bindVal), 10)
+	case int16:
+		return strconv.FormatInt(int64(bindVal), 10)
+	case uint16:
+		return strconv.FormatUint(uint64(bindVal), 10)
+	case int32:
+		return strconv.FormatInt(int64(bindVal), 10)
+	case uint32:
+		return strconv.FormatUint(uint64(bindVal), 10)
+	case int64:
+		return strconv.FormatInt(bindVal, 10)
+	case uint64:
+		return strconv.FormatUint(bindVal, 10)
+	}
+	panic("jet: Unsupported integer type: " + reflect.TypeOf(value).String())
+}
+
 func shouldQuoteIdentifier(identifier string) bool {
 	for _, c := range identifier {
 		if unicode.IsNumber(c) || c == '_' {
diff --git a/internal/jet/serializer_test.go b/internal/jet/sql_builder_test.go
similarity index 70%
rename from internal/jet/serializer_test.go
rename to internal/jet/sql_builder_test.go
index 6d2fd4a..dc4a476 100644
--- a/internal/jet/serializer_test.go
+++ b/internal/jet/sql_builder_test.go
@@ -12,8 +12,16 @@ func TestArgToString(t *testing.T) {
 	assert.Equal(t, argToString(false), "FALSE")
 
 	assert.Equal(t, argToString(int(-32)), "-32")
-	assert.Equal(t, argToString(int32(-32)), "-32")
+	assert.Equal(t, argToString(uint(32)), "32")
+	assert.Equal(t, argToString(int8(-43)), "-43")
+	assert.Equal(t, argToString(uint8(43)), "43")
+	assert.Equal(t, argToString(int16(-54)), "-54")
+	assert.Equal(t, argToString(uint16(54)), "54")
+	assert.Equal(t, argToString(int32(-65)), "-65")
+	assert.Equal(t, argToString(uint32(65)), "65")
 	assert.Equal(t, argToString(int64(-64)), "-64")
+	assert.Equal(t, argToString(uint64(64)), "64")
+	assert.Equal(t, argToString(float32(2.0)), "2")
 	assert.Equal(t, argToString(float64(1.11)), "1.11")
 
 	assert.Equal(t, argToString("john"), "'john'")
diff --git a/internal/jet/utils.go b/internal/jet/utils.go
index 67c2c6c..58394f4 100644
--- a/internal/jet/utils.go
+++ b/internal/jet/utils.go
@@ -63,6 +63,7 @@ func SerializeColumnNames(columns []Column, out *SQLBuilder) {
 	}
 }
 
+// ExpressionListToSerializerList converts list of expressions to list of serializers
 func ExpressionListToSerializerList(expressions []Expression) []Serializer {
 	var ret []Serializer
 
diff --git a/internal/testutils/test_utils.go b/internal/testutils/test_utils.go
index 1b19a20..c3d3ff0 100644
--- a/internal/testutils/test_utils.go
+++ b/internal/testutils/test_utils.go
@@ -129,7 +129,7 @@ func AssertClauseSerialize(t *testing.T, dialect jet.Dialect, clause jet.Seriali
 	}
 }
 
-// AssertClauseSerialize checks if clause serialize produces expected query and args
+// AssertDebugClauseSerialize checks if clause serialize produces expected debug query and args
 func AssertDebugClauseSerialize(t *testing.T, dialect jet.Dialect, clause jet.Serializer, query string, args ...interface{}) {
 	out := jet.SQLBuilder{Dialect: dialect, Debug: true}
 	jet.Serialize(clause, jet.SelectStatementType, &out)
diff --git a/internal/utils/utils.go b/internal/utils/utils.go
index 97ac48a..42a5c36 100644
--- a/internal/utils/utils.go
+++ b/internal/utils/utils.go
@@ -184,6 +184,7 @@ func StringSliceContains(strings []string, contains string) bool {
 	return false
 }
 
+// ExtractDateTimeComponents extracts number of days, hours, minutes, seconds, microseconds from duration
 func ExtractDateTimeComponents(duration time.Duration) (days, hours, minutes, seconds, microseconds int64) {
 	days = int64(duration / (24 * time.Hour))
 	reminder := duration % (24 * time.Hour)
diff --git a/mysql/interval.go b/mysql/interval.go
index 57c2cfc..478e9c4 100644
--- a/mysql/interval.go
+++ b/mysql/interval.go
@@ -9,10 +9,11 @@ import (
 	"github.com/go-jet/jet/internal/utils"
 )
 
-type UnitType string
+type unitType string
 
+// List of interval unit types for MySQL
 const (
-	MICROSECOND        UnitType = "MICROSECOND"
+	MICROSECOND        unitType = "MICROSECOND"
 	SECOND                      = "SECOND"
 	MINUTE                      = "MINUTE"
 	HOUR                        = "HOUR"
@@ -34,9 +35,15 @@ const (
 	YEAR_MONTH                  = "YEAR_MONTH"
 )
 
+// Interval is representation of MySQL interval
 type Interval = jet.Interval
 
-func INTERVAL(value interface{}, unitType UnitType) Interval {
+// INTERVAL creates new Interval type.
+// In a case of MICROSECOND, SECOND, MINUTE, HOUR, DAY, WEEK, MONTH, QUARTER, YEAR unit type
+// value parameter should be number. For example: INTERVAL(1, DAY)
+// In a case of other unit types, value should be string with appropriate format.
+// For example: INTERVAL("10:08:50", HOUR_SECOND)
+func INTERVAL(value interface{}, unitType unitType) Interval {
 	switch unitType {
 	case MICROSECOND, SECOND, MINUTE, HOUR, DAY, WEEK, MONTH, QUARTER, YEAR:
 		if !isNumericType(value) {
@@ -87,14 +94,15 @@ func INTERVAL(value interface{}, unitType UnitType) Interval {
 	}
 }
 
-func INTERVALe(expr Expression, unitType UnitType) Interval {
+// INTERVALe creates new Interval type from expresion and unit type.
+func INTERVALe(expr Expression, unitType unitType) Interval {
 	return jet.NewInterval(jet.ListSerializer{
 		Serializers: []jet.Serializer{expr, jet.Raw(string(unitType))},
 		Separator:   " ",
 	})
 }
 
-// INTERVALd returns a representation of duration as MySQL INTERVAL
+// INTERVALd returns a interval representation from duration
 func INTERVALd(duration time.Duration) Interval {
 	var sign int64 = 1
 	if duration < 0 {
@@ -179,7 +187,7 @@ var (
 
 func isNumericType(value interface{}) bool {
 	switch value.(type) {
-	case float64, float32, int16, int32, int64, uint16, uint32, uint64, int, uint:
+	case float64, float32, int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64:
 		return true
 	default:
 		return false
diff --git a/mysql/interval_test.go b/mysql/interval_test.go
index a7c16f8..c88b808 100644
--- a/mysql/interval_test.go
+++ b/mysql/interval_test.go
@@ -32,14 +32,18 @@ func TestINTERVAL(t *testing.T) {
 	assertDebugSerialize(t, INTERVAL("08.000100", SECOND_MICROSECOND), "INTERVAL '08.000100' SECOND_MICROSECOND")
 	assertDebugSerialize(t, INTERVAL("-08.000100", SECOND_MICROSECOND), "INTERVAL '-08.000100' SECOND_MICROSECOND")
 
-	assertDebugSerialize(t, INTERVAL(15, SECOND), "INTERVAL 15 SECOND")
-	assertDebugSerialize(t, INTERVAL(1, MICROSECOND), "INTERVAL 1 MICROSECOND")
-	assertDebugSerialize(t, INTERVAL(2, MINUTE), "INTERVAL 2 MINUTE")
-	assertDebugSerialize(t, INTERVAL(3, HOUR), "INTERVAL 3 HOUR")
-	assertDebugSerialize(t, INTERVAL(4, DAY), "INTERVAL 4 DAY")
-	assertDebugSerialize(t, INTERVAL(5, MONTH), "INTERVAL 5 MONTH")
-	assertDebugSerialize(t, INTERVAL(6, YEAR), "INTERVAL 6 YEAR")
-	assertDebugSerialize(t, INTERVAL(-6, YEAR), "INTERVAL -6 YEAR")
+	assertSerialize(t, INTERVAL(15, SECOND), "INTERVAL 15 SECOND")
+	assertSerialize(t, INTERVAL(1, MICROSECOND), "INTERVAL 1 MICROSECOND")
+	assertSerialize(t, INTERVAL(2, MINUTE), "INTERVAL 2 MINUTE")
+	assertSerialize(t, INTERVAL(3, HOUR), "INTERVAL 3 HOUR")
+	assertSerialize(t, INTERVAL(4, DAY), "INTERVAL 4 DAY")
+	assertSerialize(t, INTERVAL(5, MONTH), "INTERVAL 5 MONTH")
+	assertSerialize(t, INTERVAL(6, YEAR), "INTERVAL 6 YEAR")
+	assertSerialize(t, INTERVAL(-6, YEAR), "INTERVAL -6 YEAR")
+
+	assertSerialize(t, INTERVAL(uint(6), YEAR), "INTERVAL 6 YEAR")
+	assertSerialize(t, INTERVAL(int16(7), YEAR), "INTERVAL 7 YEAR")
+	assertSerialize(t, INTERVAL(3.5, YEAR), "INTERVAL 3.5 YEAR")
 }
 
 func TestINTERVAL_InvalidUnitType(t *testing.T) {
diff --git a/postgres/interval.go b/postgres/interval.go
index f6344fd..de659e7 100644
--- a/postgres/interval.go
+++ b/postgres/interval.go
@@ -9,12 +9,11 @@ import (
 	"time"
 )
 
-type quantityAndUnit float64
+type quantityAndUnit = float64
 
+// Interval unit types
 const (
-	pow2_32 = -4.294967296e+09
-
-	YEAR quantityAndUnit = pow2_32 + iota
+	YEAR quantityAndUnit = 123456789 + iota
 	MONTH
 	WEEK
 	DAY
@@ -33,11 +32,14 @@ type intervalExpressionImpl struct {
 	jet.ExpressionInterfaceImpl
 }
 
+// IntervalExpression is representation of postgres INTERVAL
 type IntervalExpression interface {
 	jet.IsInterval
 	jet.Expression
 }
 
+// INTERVAL creates new interval expression from the list of quantity-unit pairs.
+// For example: INTERVAL(1, DAY, 3, MINUTE)
 func INTERVAL(quantityAndUnit ...quantityAndUnit) IntervalExpression {
 	if len(quantityAndUnit)%2 != 0 {
 		panic("jet: invalid number of quantity and unit fields")
@@ -62,6 +64,7 @@ func INTERVAL(quantityAndUnit ...quantityAndUnit) IntervalExpression {
 	return newInterval
 }
 
+// INTERVALd creates interval expression from duration
 func INTERVALd(duration time.Duration) IntervalExpression {
 	days, hours, minutes, seconds, microseconds := utils.ExtractDateTimeComponents(duration)
 
diff --git a/postgres/interval_test.go b/postgres/interval_test.go
index 1d1e3de..785f1d5 100644
--- a/postgres/interval_test.go
+++ b/postgres/interval_test.go
@@ -25,6 +25,9 @@ func TestINTERVAL(t *testing.T) {
 
 	assertSerialize(t, INTERVAL(1, YEAR).IS_NOT_NULL(), "INTERVAL '1 YEAR' IS NOT NULL")
 	assertProjectionSerialize(t, INTERVAL(1, YEAR).AS("one year"), `INTERVAL '1 YEAR' AS "one year"`)
+
+	f := 5.2
+	assertSerialize(t, INTERVAL(f, YEAR), "INTERVAL '5.2 YEAR'")
 }
 
 func TestINTERVALd(t *testing.T) {