fix: use isset() when checking table property value (#52)

We can't access the `$this->table` property before initialization, so let's use `isset()` to check if the property has a value.

Reviewed-on: https://codeberg.org/vlw/php-mysql/pulls/52

README.md

@@ -15,7 +15,7 @@ which would be equivalent to the following in MySQL:
 SELECT `columns` FROM `table` WHERE `filter` ORDER BY `order_by` LIMIT `limit`;
 ```
 
-- All methods can be chained in any order (even multiple times) after a [`for()`](#for) as long as a [`select()`](#select), [`insert()`](#insert), [`update()`](#update), or [`delete()`](#delete) is the last method.
+- All methods can be chained in any order (even multiple times) after a [`from()`](#from) as long as a [`select()`](#select), [`insert()`](#insert), [`update()`](#update), or [`delete()`](#delete) is the last method.
 - Chaining the same method more than once will override its previous value. Passing `null` to any method that accepts it will unset its value completely.
 
 ## Install from composer

src/MySQL.php

@@ -35,7 +35,7 @@
 		*/
 
 		private function throw_if_no_table() {
-			if (!$this->table) {
+			if (!isset($this->table)) {
 				throw new Exception("No table name defined");
 			}
 		}
@@ -81,7 +81,7 @@
 			since: "3.5.7",
 		)]
 		public function for(string $table): self {
-			$this->from($table);
+			return $this->from($table);
 		}
 
 		// Create a WHERE statement from filters
@@ -163,17 +163,8 @@
 				return $this;
 			}
 
-			// Set LIMIT without range directly as integer
-			if (is_int($limit)) {
-				$this->limit = $limit;
-				return $this;
-			}
-
-			// No offset defined, set limit property directly as string
-			if (is_null($offset)) {
-				$this->limit = (string) $limit;
-				return $this;
-			}
+			// Coerce offset to zero if no offset is defined
+			$offset = $offset ?? 0;
 
 			// Set limit and offset as SQL CSV
 			$this->limit = "{$offset},{$limit}";
@@ -277,9 +268,14 @@
 			$this->throw_if_no_table();
 
 			// Set DELETE WHERE conditions from arguments
-			$this->where(...$conditions);
+			if ($conditions) {
+				$this->where(...$conditions);
+			}
 
-			$sql = "DELETE FROM `{$this->table}` WHERE {$this->filter_sql}";
+			// Get array of SQL WHERE string and filter values
+			$filter_sql = !is_null($this->filter_sql) ? " WHERE {$this->filter_sql}" : "";
+
+			$sql = "DELETE FROM `{$this->table}`{$filter_sql}";
 			return $this->execute_query($sql, self::to_list_array($this->filter_values));
 		}