SQL 的无效参数查询是否从 Excel - VBA 选择空单元格

Question

Instead of using Nested If statements, I was wondering if there is a way to void out parts of a string query if cell value is left blank.

Cell structure is as below:

Cell values from these parameters will get passed into vba code that queries a database. Ideally I don't want to create an individual query for each selection type - and I have it dynamically querying from location already. I want to extend the query to include possible combinations of start, end, value >, value <, while also making it so that if cell value is left blank, then ignore that parameter. So say

SELECT * 
from database 
WHERE location = 'cell_loc' 
AND Value >= 'cell_value' 
AND Value <= 'cell_value' 
AND Start >= 'cell_date' 
AND End <= 'cell_date'

Now imagine that Start is left blank, meaning I want to query from first data point in the database:

I could write a nested if to handle this, but was wondering if there was a way to void out a query parameter so that I could just have a single query fed to database with different parameters changing based off cell data?

Something along the lines of:

SELECT * 
from database 
WHERE location = 'cell_loc' 
AND Value >= 'cell_value' 
AND Value <= 'cell_value' 
AND Start >= 'cell_date' --> this would be voided out
AND End <= 'cell_date'

Answer 1

Using the coalesce() function you can put an equality condition in your WHERE clause. This is a common SQL trick to deal with null parameters or null values in the data.

SELECT * 
from database 
WHERE location = 'cell_loc' 
AND Value >= 'cell_value' 
AND Value <= 'cell_value' 
AND (Start >= 'cell_date' OR Start = coalesce('cell date', Start))
AND End <= 'cell_date'

Answer 2

Here's a very basic example:

Sub Tester()
    Dim sWhere As String, sql As String
    
    sql = "Select * from myTable "
    
    sWhere = ""
    BuildWhere sWhere, "id = <v>", Range("A5")
    BuildWhere sWhere, "pName = '<v>'", Range("B5")
    BuildWhere sWhere, "pDate > '<v>'", Range("C5")
    
    If Len(sWhere) > 0 Then
        sql = sql & " where " & sWhere
        Debug.Print sql
        'run query
    Else
        'don't run if no criteria ?
    End If

End Sub

'add a where clause only if `c` has a value
Sub BuildWhere(ByRef sWhere As String, test As String, c As Range)
    Dim v
    v = Trim(c.Value)
    If Len(v) > 0 Then
        If Len(sWhere) > 0 Then sWhere = sWhere & vbLf & " and "
        sWhere = sWhere & Replace(test, "<v>", v)
    End If
End Sub