INSERT INTO Tab1 (Col1, Col2,.....)
SELECT Col1, Col2......
FROM Tab3
WHERE .....

CREATE TABLE [Tab1] 
(
    [ClientContextID] INT IDENTITY (1, 1)	NOT NULL,
    [ClientID]        UNIQUEIDENTIFIER		NOT NULL,
    [ContextID]       INT				NOT NULL,
    [SessionID]       INT				NULL,
    [ToRefresh]       BIT			NOT NULL
);

ALTER TABLE [Tab1]
    ADD CONSTRAINT [PK_Tab1] PRIMARY KEY CLUSTERED ([ClientContextID] ASC);

ALTER TABLE [Tab1]
    ADD CONSTRAINT [FK_Tab1_Tab2]  FOREIGN KEY ([SessionID]) 
    REFERENCES [Tab2] ([SessionID]) ON DELETE CASCADE ON UPDATE NO ACTION;

CREATE INDEX [IX_Tab1]
    ON [Tab1] (ClientID ASC, SessionID ASC) INCLUDE (ClientContextID, ToRefresh, ContextID);


CREATE TABLE [Tab2]
(
    [SessionID]           	INT IDENTITY (1, 1) NOT NULL,
    [PatientID]           	CHAR (12)     	 NOT NULL,
    [Active]              	BIT           		NOT NULL,
    [Start]               	DATETIME      	 NOT NULL,
    [End]                 	DATETIME      	 NULL,
   ...............................................
);

ALTER TABLE [Tab2]
    ADD CONSTRAINT [PK_Tab2] PRIMARY KEY CLUSTERED ([SessionID] ASC);