feat: generate test substrait plans & basic parse

src/Backend/opti-sql-go/operators/project/csv.go

@@ -204,7 +204,6 @@ func parseDataType(sample string) arrow.DataType {
 	if sample == "" || strings.EqualFold(sample, "NULL") {
 		return arrow.BinaryTypes.String
 	}
-
 	// Boolean
 	if sample == "true" || sample == "false" {
 		return arrow.FixedWidthTypes.Boolean

src/Backend/opti-sql-go/substrait/expr.md

@@ -0,0 +1,206 @@
+---
+## Expressions
+
+Expressions are encoded as **tagged objects** using `expr_type`.
+They are evaluated row-wise against a record batch and return an Arrow array.
+
+When applicable, expressions **may include an explicit Arrow type** to avoid inference ambiguity.
+---
+
+## `Valid Literal Types`
+
+```bash
+"int"
+"string"
+"boolean"
+"float64"
+```
+
+## `Valid Binary Operators`
+
+```bash
+"Addition"
+"Subtraction"
+"Multiplication"
+"Division"
+# comparison
+"Equal"
+"NotEqual"
+"LessThan"
+"LessThanOrEqual"
+"GreaterThan"
+"GreaterThanOrEqual"
+# logical
+"And"
+"Or"
+```
+
+## `Valid Scalar functions`
+
+```bash
+"Upper"
+"Lower"
+"Abs"
+"Round"
+```
+
+## `Valid Aggregations functions`
+
+```bash
+"Sum"
+"Count"
+"Avg"
+"Min"
+"Max"
+```
+
+## `ColumnResolve`
+
+Resolves a column from the input batch.
+
+```bash
+{
+  "expr_type": "ColumnResolve",
+  "name": "a"
+}
+```
+
+---
+
+## `LiteralResolve`
+
+Represents a constant literal value.
+
+```bash
+{
+  "expr_type": "LiteralResolve",
+  "value": 10,
+  "lit_type": "int"
+}
+```
+
+### Notes
+
+- `lit_type` is **optional**
+- When provided, it must be a valid Arrow primitive type
+- If omitted, the engine may infer the type
+
+---
+
+## `BinaryExpr`
+
+Applies a binary operator to two expressions.
+
+```bash
+{
+  "expr_type": "BinaryExpr",
+  "op": "GreaterThan", # or any (valid) binary operator
+  "left": {
+    "expr_type": "ColumnResolve",
+    "name": "a"
+  },
+  "right": {
+    "expr_type": "LiteralResolve",
+    "value": 10,
+    "lit_type": "int"
+  }
+}
+```
+
+- Comparison and logical operators must return a boolean array
+- Left and right expressions must resolve to compatible Arrow types
+
+---
+
+## `ScalarFunction`
+
+Applies a scalar function element-wise.
+
+```bash
+{
+  "expr_type": "ScalarFunction",
+  "func": "Upper", # or any (Valid) scalar function
+  "args": [
+    {
+      "expr_type": "ColumnResolve",
+      "name": "name"
+    }
+  ]
+}
+```
+
+---
+
+## `Alias`
+
+Attaches a name to an expression.
+
+```bash
+{
+  "expr_type": "Alias",
+  "expr": {
+    "expr_type": "ColumnResolve",
+    "name": "a"
+  },
+  "name": "alias_a"
+}
+```
+
+- Alias affects **naming only**
+- Evaluation result is unchanged
+
+---
+
+## `CastExpr`
+
+Casts the result of an expression to a specific Arrow type.
+
+```bash
+{
+  "expr_type": "CastExpr",
+  "expr": {
+    "expr_type": "ColumnResolve",
+    "name": "a"
+  },
+  "to_type": "Float64"
+}
+```
+
+---
+
+## `NullCheckExpr`
+
+Checks whether values are null or non-null.
+
+```bash
+{
+  "expr_type": "NullCheckExpr",
+  "expr": {
+    "expr_type": "ColumnResolve",
+    "name": "a"
+  },
+  "is_null": true
+}
+```
+
+- Produces a boolean mask
+
+---
+
+## Expression Type Enum
+
+`expr_type` is a **closed enum**.
+
+```bash
+ColumnResolve
+LiteralResolve
+BinaryExpr
+ScalarFunction
+Alias
+CastExpr
+NullCheckExpr
+```
+
+Each expression object **must** contain exactly one `expr_type`.
+
+---