# Tutor profile: Greg B.

## Questions

### Subject: SQL Programming

Describe the difference between a 'LEFT JOIN' and an 'INNER JOIN' in SQL.

At a general level, the difference between a left join and an inner join is the data that is being pulled into the output. The easiest way to think about the difference is with a Venn Diagram, with table 1 in the 'FROM' clause being the circle on the left and table 2 in the 'JOIN' clause being the table on the right. The overlap between the two is what is pulled when using an inner join. The data that the two tables share in common is produced in the output. A left join then takes all of the data in the 'FROM' clause (table 1) and also everything that the tables have in common (the intersection of the two tables in the Venn diagram). It may also help to understand that another type of join exists. A 'RIGHT JOIN' takes everything from the table 2 in the 'JOIN' clause (right circle of Venn diagram) and everything that the tables have in common. For example: SELECT * FROM table1 LEFT JOIN table2 ON table1.Field = table2.Field. This query will produce results that have everything from table 1 as well as the data that is shared between the table 1 and table 2.

### Subject: Microsoft Excel

Describe the two types of references in Excel.

There are two types of references in Microsoft Excel: Absolute and Relative. A relative is the more common of the two. Think of a relative reference as a cell being unlocked and an absolute reference as being locked. Excel uses the '$' to lock in cells. You notice this when you drag formulas down and across. A formula in cell C1 that reads '=A1 + B1' will = 'A2 + B2' when the formula in C1 is filled down to C2. Using the absolute reference can change this functionality. If you 'lock' cell A1 and B1 and fill the formula down to C2, the value in C1 and C2 will be the same. For example, the formula in C1 would read '=$A$1 + $B$1'. Fill this formula down to C2 and you get the same formula (=A$1 + $B$1). The absolute reference is a powerful feature in Excel that can come in handy while working with various data sets.

### Subject: Algebra

Evaluate the following equation to solve for x: 30 - 12 / 3 * 2 = x Show work and explain each step.

1) Begin by simplifying the equation 30 - 4 * 2 = x 2) Simplify even further 30 - 8 = x 3) Simplify one final time to solve for x 22 = x Final Answer

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