SQL Descending ordered LEFT JOIN subquery issue - sql

Question

I have the following query.
SELECT r1.*,
r2.vlag54,
r2.vlag55
FROM [rxmon].[dbo].[a] AS r1
LEFT JOIN [rxmon].[dbo].[b] AS r2
ON r2.artikelnummer = r1.drug_id
LEFT JOIN (SELECT *
FROM [rxmon].[dbo].[c]) AS r3
ON r3.pid = r1.patient_id
WHERE r3.obx_id = 20937
AND Cast(r3.obx_datetime AS DATE) = Cast(Getdate() - 1 AS DATE)
AND r1.patient_id = 7092425
AND obx_value < CASE
WHEN r2.vlag54 = 1 THEN 30
WHEN r2.vlag55 = 1 THEN 50
END
AND r2.vlag54 = CASE
WHEN r3.obx_value < 30 THEN 1
ELSE 0
END
AND r2.vlag55 = CASE
WHEN r3.obx_value BETWEEN 30 AND 50 THEN 1
ELSE 0
END
ORDER BY obx_datetime DESC;
The problem is that table C can contain multiple records based on de PID join. This generates the same records because of the multiple records on table C.
The table C needs to e joined as the latest record only so just 1 of C. That way the table A record will not be repeated.
I tried TOP 1 and order by but that can't be used in subquery.
-- TABLE A
CREATE TABLE [dbo].[A]
[EVS_MO_ID] [bigint] NOT NULL,
[DRUG_ID] [varchar](50) NOT NULL,
[ATC_CODE] [varchar](15) NULL,
[DRUG_NAME] [varchar](1024) NULL,
[PATIENT_ID] [varchar](50) NOT NULL,
[PATIENT_LOCATION] [varchar](10) NULL,
[MO_DATE] [datetime2](7) NOT NULL,
[MO_START_DATE] [datetime2](7) NOT NULL,
[MO_STOP_DATE] [datetime2](7) NULL,
[ROUTE] [varchar](50) NULL,
[MEDICATION_CONTAINER] [smallint] NULL,
[PRESCRIBING_DOCTOR_NAME] [varchar](50) NULL,
[PRESCRIBING_DOCTOR_SURNAME] [varchar](50) NULL,
[MO_ACTIVE] [bit] NOT NULL,
CONSTRAINT [PK_MedicationOrders] PRIMARY KEY CLUSTERED
(
[EVS_MO_ID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = ON, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
INSERT INTO [dbo].[A]
VALUES
(5411409,'97941689', 'B01AB06','NADROPARINE 0.8ML','7092425','ANBC', '2015-12-15 20:58:06.2030000',
'2015-12-16 00:00:00.0000000', '', 'IV', 1, 'GEORGE','LAST', 1);
-- TABLE B
CREATE TABLE [dbo].[B](
[ID] [int] IDENTITY(1,1) NOT NULL,
[ARTIKELNUMMER] [varchar](50) NOT NULL,
[VLAG54] [bit] NULL,
[VLAG55] [bit] NULL CONSTRAINT [DF_Table_1_VLAG50] DEFAULT ((0)),
[VLAG100] [bit] NULL CONSTRAINT [DF_ArtikelVlaggen_VLAG100] DEFAULT ((0)),
CONSTRAINT [PK_B] PRIMARY KEY CLUSTERED
(
[ID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
INSERT INTO [dbo].[B]
([ARTIKELNUMMER]
,[VLAG54]
,[VLAG55]
,[VLAG100])
VALUES
('97941689', 1,0,1);
-- TABLE C
CREATE TABLE [dbo].[C](
[ID] [int] IDENTITY(1,1) NOT NULL,
[OBX_DATETIME] [datetime2](7) NOT NULL,
[PID] [int] NOT NULL,
[DEPARTMENT] [varchar](8) NOT NULL,
[OBX_ID] [int] NOT NULL,
[OBX_VALUE] [decimal](5, 2) NOT NULL,
[OBX_UNITS] [varchar](10) NULL,
[REF_RANGE] [varchar](40) NULL,
[FLAG] [varchar](2) NULL,
CONSTRAINT [PK_C] PRIMARY KEY CLUSTERED
(
[ID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
INSERT INTO [dbo].[C]
([OBX_DATETIME]
,[PID]
,[DEPARTMENT]
,[OBX_ID]
,[OBX_VALUE]
,[OBX_UNITS]
,[REF_RANGE]
,[FLAG])
VALUES
('2015-12-15 14:01:00.0000000',7092425, '8NAH', 20937, 27.00, 'mL/min', '> 60', 'L');
INSERT INTO [dbo].[C]
([OBX_DATETIME]
,[PID]
,[DEPARTMENT]
,[OBX_ID]
,[OBX_VALUE]
,[OBX_UNITS]
,[REF_RANGE]
,[FLAG])
VALUES
('2015-12-15 06:30:00.0000000',7092425, '6ZPA', 20937, 28.00, 'mL/min', '> 60', 'L');

Answer 1

This will order them by OBX_DATETIME and take only the first one:
...
LEFT JOIN (
SELECT pid, obx_id, obx_datetime, obx_value
, n = ROW_NUMBER() over(PARTITION BY pid ORDER BY obx_datetime desc)
FROM [rxmon].[dbo].[c]
) AS r3
ON r3.pid = r1.patient_id and r3.n = 1
...
If OBX_DATETIME are inserted incrementaly (newer date only), you can order by ID instead.
This SQL Fiddle with your query and sample data/tables returns 2 rows: http://sqlfiddle.com/#!3/df36c/2/0
This SQL Fiddle with the new subquery returns 1 row: http://sqlfiddle.com/#!3/df36c/1/0
You are using a LEFT JOIN on r3 but have also have r3 in your WHERE clause with equal operator:
WHERE r3.obx_id = 20937
AND Cast(r3.obx_datetime AS DATE) = Cast(Getdate() - 1 AS DATE)
It will remove NULL value from the left join on r3. Perhaps you should also move it to the sub query or use INNER JOIN.
You should also avoind using the DB name in your query unless this query is run from another DB on the same server. This will be fine:
SELECT ... FROM [dbo].[a] AS r1 ...
Using SELECT * is also a bad habit. You should list only the columns your code will use.

Answer 2

try this.... #Shift
SELECT r1.*,
r2.vlag54,
r2.vlag55
FROM [dbo].[a] AS r1
LEFT JOIN [dbo].[b] AS r2
ON r2.artikelnummer = r1.drug_id
LEFT JOIN (
SELECT
ROW_NUMBER() OVER (PARTITION BY pid ORDER BY id DESC) RN,
c.*
FROM C
) r3
ON r3.pid = r1.patient_id AND r3.RN = 1
WHERE r3.obx_id = 20937
AND Cast(r3.obx_datetime AS DATE) = Cast(Getdate() - 1 AS DATE)
AND r1.patient_id = 7092425
AND obx_value < CASE
WHEN r2.vlag54 = 1 THEN 30
WHEN r2.vlag55 = 1 THEN 50
END
AND r2.vlag54 = CASE
WHEN r3.obx_value < 30 THEN 1
ELSE 0
END
AND r2.vlag55 = CASE
WHEN r3.obx_value BETWEEN 30 AND 50 THEN 1
ELSE 0
END
ORDER BY obx_datetime DESC;