Blaze symbol fetching the wrong fields

Suppose I have this

```
from blaze import Data, compute, symbol
from odo import odo
import pandas

df = Data('postgresql://jeffrey04:abc123@localhost:5432/meow::woof',
dshape="""
var * {a: int64,
b: string,
c: string,
d: string,
e: string,
f: string,
g: string,
h: string,
i: string,
j: string,
k: string,
l: string,
m: string,
n: string,
o: string,
p: string}
""",
name=meow)
```

So I was trying to get all the `k` where none of them contain an empty string

```
want_this = odo(df[df.k != ''].k, pandas.Series)
```

but then when I inspect the data, I don't get `k`, but `j` instead, so I checked the sql issued by blaze by doing this

```
print(compute(want_this))
```

yields

```
SELECT meow.j
FROM meow
WHERE meow.state != %(k_1)s
```

which clearly not what I was expecting.

I also did this

```
res = resource('postgresql://jeffrey04:abc123@localhost:5432/meow::woof')
sym = symbol('s',
"""
var * {a: int64,
b: string,
c: string,
d: string,
e: string,
f: string,
g: string,
h: string,
i: string,
j: string,
k: string,
l: string,
m: string,
n: string,
o: string,
p: string}
""")
odo(compute(sym[sym.k != ''].k, res), pandas.Series)
```

also returned the same output (getting `j` instead of `k`)