Why I get this error using TSQL to find a connected graph?

Question

nodes(nodeID int) is a list of all nodes. edges(fromNodeID int, toNodeID int) is the relationship between two nodes. Assume the graph is undirected, find all the connected components.

CREATE PROCEDURE getGraph
    AS BEGIN
        CREATE TABLE graphs (node int, id int);
        DECLARE @graphID int;
        SET @graphID = 0;
    
        WHILE ((SELECT COUNT(*) FROM graphs) < (SELECT COUNT(*) FROM nodes))
        BEGIN
            CREATE TABLE currentGraph (node int);
            CREATE TABLE temp(node int);
            DECLARE @start int;
            SET @start = (SELECT TOP (1) n.paperID
                          FROM nodes n
                          WHERE n.paperID NOT IN (SELECT * FROM graphs));
            INSERT INTO currentGraph VALUES (@start);
            INSERT INTO temp (node) VALUES (
                SELECT e.citedPaperID
                FROM currentGraph cg, edges e
                WHERE cg.node = e.paperID
                );
    
            /* If there is any new node, keep searching for current graph*/
            WHILE ((SELECT COUNT(*)
                    FROM temp
                    WHERE temp.node NOT IN (SELECT * FROM currentGraph)) <> 0)
            BEGIN
                INSERT INTO currentGraph (node) VALUES (
                    SELECT t.node
                    FROM temp t
                    WHERE t.node NOT IN (SELECT * FROM currentGraph)
                    );
                DELETE FROM temp;
    
                INSERT INTO temp (node) VALUES (
                SELECT e.citedPaperID
                FROM currentGraph cg, edges e
                WHERE cg.node = e.paperID
                );
            END
            SET @graphID = @graphID + 1;
            INSERT INTO graphs (node, id) VALUES ((SELECT DISTINCT cg.node FROM currentGraph cg), @graphID);
        END
    END

Error message:

[2021-10-02 21:52:07] [S1000][156] Incorrect syntax near the keyword 'SELECT'. [2021-10-02 21:52:07] [42000][102] Incorrect syntax near ')'.
[2021-10-02 21:52:07] [S1000][156] Incorrect syntax near the keyword 'SELECT'. [2021-10-02 21:52:07] [42000][102] Incorrect syntax near ')'.
[2021-10-02 21:52:07] [S1000][156] Incorrect syntax near the keyword 'SELECT'. [2021-10-02 21:52:07] [42000][102] Incorrect syntax near ')'.

Answer 1

The error message is caused by the incorrect syntax of the INSERT statement.

You can use one of the following:

INSERT INTO YourTable (SomeColumn) VALUES (constant);
INSERT INTO YourTable (SomeColumn, OtherColumn) SELECT FirstColumn, SecondColumn FROM AnotherTable;
INSERT INTO YourTable (SomeColumn) VALUES ((SELECT SingleColumn FROM AnotherTable));

(I did not look at the correctness of the rest of the code, so I cannot confirm if it solves your problem after fixing the syntax error)